Method for developing a hydrocarbon reservoir (variants) and complex for carrying out said method (variants)

ABSTRACT

The invention relates to oil and natural gas production and can be used for recovering hydrocarbons from hydrocarbon-bearing formations, for example, from oil-bearing formations, or, for example, from gas-condensate reservoirs. A method for recovery of hydrocarbons from a hydrocarbon-bearing formation, comprises: recovering a hydrocarbon-containing fluid through at least one production well, separating at least a part of a gaseous mixture from the fluid, injecting a gas through injection well. The separated gaseous mixture (all or a part of it) is combusted with air, which is used as oxidant, in a power plant, and, exhaust gases resulting from said combustion, which comprise nitrogen and carbon dioxide, are discharged from the power plant. Said air and the separated gaseous mixture are mixed and a gas-air mixture resulting from said mixing is compressed prior to said combustion, or the gas-air mixture is ignited during said compression. In the alternative embodiment of the invented method said air and the separated gaseous mixture are compressed and then are mixed to produce the gas-air mixture prior to said combustion, or the gas-air mixture is ignited, as soon as it is mixed. In both embodiments of the invented method the exhaust gases are compressed and used as an injection gas.

[0001] The invention relates to oil and natural gas production and canbe used for recovering hydrocarbons from hydrocarbon-bearing formations,for example, from oil-bearing formations, or, for example, fromgas-condensate reservoirs, or natural gas reservoirs, wherein naturalgas is wet gas.

[0002] There is a well-known method of recovering oil from anoil-bearing formation, according to which the formation is penetrated bywells, and, an oil-gas mixture is recovered through the production wellsby means of heating the oil-gas mixture in the formation/see: the USSRInventors Certificate No1629504 A1, cl. E21B 43/24, published on 23 Feb.1991/.

[0003] Among the disadvantages of the known recovery method there is arelatively low effectiveness, because a portion of the oil-gas mixtureis burnt to heat up the oil in the formation. Besides, to support theburning process it is necessary to supply the oxygen containing mixtureresulting in additional energy consumption.

[0004] The closest in its technical essence and the achieved result, isthe method of recovering hydrocarbons from a hydrocarbon-bearingformation, wherein hydrocarbon-containing fluid is recovered from theformation through at least one production well; all gaseous mixture (inthe form of hydrocarbon gas) or a portion of it, is separated from thefluid; gas (e.g.: nitrogen and carbon dioxide) is injected into theformation through at least one injection well/see: Petersen, A. Oilrecovery experiments with N₂ and CO₂, Inzhener-Neftianik, 1978, No 11,p. 21/.

[0005] The disadvantage here is that the increase in production ofhydrocarbons is achieved by significant energy consumption, wherein theinjected gas and the energy are not produced but only consumed.

[0006] The objects of this invention are: to increase recovery ofhydrocarbons, while maintaining a high rate of energy effectiveness ofthe process of the hydrocarbons production from a hydrocarbon-bearingformation, and, besides, to increase the amount of produced energy, andto provide an environmentally safer hydrocarbons production process fromthe hydrocarbon-bearing formation.

[0007] Technical result according to the first embodiment of theinvented method, comprising: recovering a hydrocarbon-containing fluidthrough at least one production well, separating at least a part of agaseous mixture from the fluid, injecting a gas through at least oneinjection well, is achieved due to the fact, that

[0008] at least a part of the separated gaseous mixture is combustedwith air, which is used as oxidant, in a power plant, said air and saidat least a part of the separated gaseous mixture are mixed and a gas-airmixture resulting from said mixing is compressed prior to saidcombustion, or the gas-air mixture is ignited during said compression,exhaust gases resulting from said combustion, which comprise nitrogenand carbon dioxide as their components, are discharged from the powerplant, and

[0009] at least a part of the exhaust gases is compressed and then isused as at least a part of said injection gas;

[0010] electrical energy and/or heat energy are/is produced in the powerplant when said combustion of said at least a part of the separatedgaseous mixture is realized;

[0011] water is injected through at least one injection well, saidinjection gas and the water being injected simultaneously or one afteranother;

[0012] said air and said at least a part of the separated gaseousmixture are mixed in the power plant and/or the gas-air mixture iscompressed in the power plant;

[0013] the gas-air mixture is compressed during said mixing and/or aftersaid mixing;

[0014] a pressure of the gas-air mixture is established according to thecomposition of said at least a part of the separated gaseous mixturewhen the gas-air mixture is being compressed;

[0015] said at least a part of the separated gaseous mixture and/or saidair are/is compressed prior to said mixing;

[0016] the gas-air mixture is heated prior to said compression and/orsaid at least a part of the separated gaseous mixture is heated prior tosaid mixing;

[0017] a ratio between said air contained in the gas-air mixture andcombustible constituents of the gas-air mixture is maintained so, thatthe gas-air mixture comprises said air in the amount which istheoretically necessary for oxidizing the combustible constituents ofthe gas-air mixture, or the gas-air mixture comprises more of said air,than it is theoretically necessary for oxidizing the combustibleconstituents of the gas-air mixture;

[0018] a ratio between said air contained in the gas-air mixture andcombustible constituents of the gas-air mixture is maintained so, thatthe gas-air mixture comprises less of said air, than it is theoreticallynecessary for oxidizing the combustible constituents of the gas-airmixture;

[0019] the gas-air mixture comprises said at least a part of theseparated gaseous mixture, said air and a part of the exhaust gases;

[0020] said at least a part of the separated gaseous mixture and/or saidair are/is mixed with a part of the exhaust gases prior to production ofthe gas-air mixture;

[0021] the gas-air mixture is mixed with a part of the exhaust gasesprior to said compression of the gas-air mixture or during saidcompression of the gas-air mixture;

[0022] said at least a part of the exhaust gases is previouslycompressed, after which moisture is removed, and then said at least apart of the exhaust gases is additionally compressed and is subsequentlyused as said at least a part of said injection gas;

[0023] the water is heated by the heat and/or the electrical energyprior to the water being injected;

[0024] said injection gas is heated by the heat and/or the electricalenergy prior to said injection gas being injected;

[0025] a pressure and/or a temperature of said injection gas and/or ofthe water are/is established according to a geological-and-physicalcharacteristic and a development stage of the formation;

[0026] a composition and a quantity of said injection gas areestablished according to a geological-and physical characteristic and adevelopment stage of the formation; specifically, said injection gas istreated to a desirable composition by reducing concentration of nitrogenin said at least a part of the exhaust gases;

[0027] said at least a part of the separated gaseous mixture is treatedfor removal of moisture and/or corrosive substances prior to saidmixing;

[0028] liquid or gaseous substances, including combustible substances,are added into the gas-air mixture prior to said combustion;

[0029] said injection gas is treated for removal of moisture and/orcorrosive substances prior to said injection;

[0030] said injection gas is injected through at least one productionwell;

[0031] said at least a part of the separated gaseous mixture isseparated to produce nitrogen and/or carbon dioxide, and then thenitrogen and/or the carbon dioxide are/is mixed with said at least apart of the exhaust gases, whereupon, the resulting mixture is used assaid at least a part of said injection gas.

[0032] Technical result according to the second embodiment of theinvented method, comprising:

[0033] recovering a hydrocarbon-containing fluid through at least oneproduction well

[0034] separating at least a part of a gaseous mixture from the fluid,

[0035] injecting a gas through at least one injection well

[0036] is achieved due to the fact, that

[0037] at least a part of the separated gaseous mixture is combustedwith air, which is used as oxidant, in a power plant, said air and saidat least a part of the separated gaseous mixture are compressed and thenare mixed to produce a gas-air mixture prior to said combustion, or thegas-air mixture is ignited, as soon as it is mixed, exhaust gasesresulting from said combustion, which comprise nitrogen and carbondioxide as their components, are discharged from the power plant, and

[0038] at least a part of the exhaust gases is compressed and then isused as at least a part of said injection gas;

[0039] electrical energy and/or heat energy are/is produced in the powerplant when said combustion of said at least a part of the separatedgaseous mixture is realized;

[0040] water is injected through at least one injection well, saidinjection gas and the water being injected simultaneously or one afteranother;

[0041] said air and said at least a part of the separated gaseousmixture are mixed and/or compressed in the power plant;

[0042] a pressure of said air and a pressure of said at least a part ofthe separated gaseous mixture are established according to thecomposition of said at least a part of the separated gaseous mixture,when said compression of said air and of said at least a part of theseparated gaseous mixture is being realized;

[0043] said at least a part of the separated gaseous mixture is heatedprior to said compression;

[0044] a ratio between said air contained in the gas-air mixture andcombustible constituents of the gas-air mixture is maintained so, thatthe gas-air mixture comprises said air in the amount, which istheoretically necessary for oxidizing the combustible constituents ofthe gas-air mixture, or the gas-air mixture comprises more of said air,than it is theoretically necessary for oxidizing the combustibleconstituents of the gas-air mixture;

[0045] a ratio between said air contained in the gas-air mixture andcombustible constituents of the gas-air mixture is maintained so, thatthe gas-air mixture comprises less of said air, than it is theoreticallynecessary for oxidizing the combustible constituents of the gas-airmixture; the gas-air mixture comprises said at least a part of theseparated gaseous mixture, said air and a part of the exhaust gases;

[0046] said at least a part of the separated gaseous mixture and/or saidair are/is mixed with a part of the exhaust gases prior to saidcombustion or during ignition of the gas-air mixture; the gas-airmixture is mixed with a part of the exhaust gases prior to saidcombustion or during ignition of the gas-air mixture;

[0047] said at least a part of the exhaust gases is previouslycompressed, after which moisture is removed, and then said at least apart of the exhaust gases is additionally compressed and is subsequentlyused as said at least a part of said injection gas; the water is heatedby the heat and/or the electrical energy prior to the water beinginjected;

[0048] said injection gas is heated by the heat and/or the electricalenergy prior to said injection gas being injected;

[0049] a pressure and/or a temperature of said injection gas are/isestablished according to a geological-and-physical characteristic and adevelopment stage of the formation;

[0050] a composition and a quantity of said injection gas areestablished according to a geological-and physical characteristic and adevelopment stage of the formation; specifically, said injection gas istreated to a desirable composition by reducing concentration of nitrogenin said at least a part of the exhaust gases;

[0051] said at least a part of the separated gaseous mixture is treatedfor removal of moisture and/or corrosive substances prior to saidcompression;

[0052] liquid or gaseous substances, including combustible substances,are added into the gas-air mixture prior to said combustion;

[0053] said injection gas is treated for removal of moisture and/orcorrosive substances prior to said injection;

[0054] said injection gas is injected through at least one productionwell;

[0055] said at least a part of the separated gaseous mixture isseparated to produce nitrogen and/or carbon dioxide, and then thenitrogen and/or the carbon dioxide are/is mixed with said at least apart of the exhaust gases, whereupon, the resulting mixture is used assaid at least a part of said injection gas;

[0056] a pressure and/or a temperature of the water are/is establishedaccording to a geological-and-physical characteristic and a developmentstage of the formation.

[0057] Exhaust gas injection into a hydrocarbon-bearing formation iswell known, including, injection of a mixture of steam and exhaustgases/see: RU patent No 2046933 C1, cl. E21B 43/24, published on 27 Oct.1995/. However, said technical result cannot be achieved, because energyis consumed to produce the mixture of the steam and the exhaust gases.Also, a gaseous mixture separated from recovered fluid is not used toproduce the mixture of the steam and the exhaust gases. Furthermore, theeffective utilization of the separated gaseous mixture is not realized.Injection of exhaust gases of the power plant results in reduced qualityof a gaseous mixture separated from the produced fluid, owing toincreased concentration of the exhaust gases of the power plant. Toproduce hydrocarbons from the separated gaseous mixture it becomesnecessary to employ gas separation equipment (which leads to increasedenergy consumption). According to the known method/see: the USSRInventors Certificate No 1729300 A3, cl. E21B 43/24, published on 23Apr. 1992/, a gaseous mixture is separated from recovered fluid,electrical energy and steam are produced, a portion of the steam isinjected into a hydrocarbon-bearing formation. However, said technicalresult cannot be achieved, because energy is consumed to produce theportion of the steam, which is to be injected. Furthermore, exhaustgases are not used for injection into the formation, wherein the exhaustgases are produced by splitting a mixture of the rest of the steam andmethane (the methane is contained in the gaseous mixture separated fromthe fluid). Said technical result in the invented method is achieved dueto the fact that together with other essential features disclosed in theclaims, at least a part of the separated gaseous mixture is combustedwith air, which is used as oxidant, in a power plant, and, exhaust gasesresulting from said combustion, which comprise nitrogen and carbondioxide as their components, are discharged from the power plant,wherein

[0058] said air and said at least a part of the separated gaseousmixture are mixed to produce a gas-air mixture, the gas-air mixture iscompressed prior to said combustion or the gas-air mixture is ignitedduring said compression (in the first embodiment of the inventedmethod);

[0059] said air and said at least a part of the separated gaseousmixture are compressed and then are mixed to produce gas-air mixtureprior to said combustion or the gas-air mixture is ignited, as soon asit is mixed (in the second embodiment of the invented method).

[0060] This will allow, when injecting a working substance comprisingnitrogen and carbon dioxide (the working substance is a gas, comprisingat least a part of exhaust gases of the power plant), for example, intoan oil-bearing formation, to increase oil recovery from productionwells. Also, the production of a gaseous mixture separated from therecovered oil-containing fluid (within the limits of a given example wewill call the gaseous mixture, separated from the recoveredoil-containing fluid, “hydrocarbon gas”) will be increased. Accordingly,this will allow to increase the hydrocarbon gas supply into the powerplant. This will provide for a possibility to increase an amount ofenergy generated by the power plant (for example: a) mechanical energyand/or electrical energy; or b) mechanical energy and/or electricalenergy and heat energy; or c) mechanical energy and heat energy and/orelectrical energy) and an amount of the produced working substance. Theincrease of the production of the hydrocarbon gas (accordingly, theincrease of the amount of the energy generated by the power plant andthe increase of the amount of the produced working substance)corresponds not only with the increase in the oil recovery, that is, theincrease of the production of the hydrocarbon gas is not only inproportion with the increase in the oil recovery, but it is alsoconditioned by the increase of the gas factor, since gaseoushydrocarbons are extracted from an oil-containing fluid present in theformation, when the formation oil-containing fluid is affected upon bythe working substance (comprising nitrogen and carbon dioxide). Forexample, an increase of a gas factor was achieved, when formationoil-containing fluid was affected upon by carbon dioxide, and itresulted in 30-35% increase of the produced gaseous hydrocarbons amountand, accordingly, the value of the gas factor increased. Said 30-35%increase of the value of the gas factor has been achieved, due to theability of the carbon dioxide to extract gaseous hydrocarbons fromoil-containing fluid. An amount of gaseous hydrocarbons extracted fromheavy oil (said oil, after its separation from formation oil-containingfluid has been affected upon by carbon dioxide) may be equal to anamount of gaseous hydrocarbons, separated from the formationoil-containing fluid/see: Mirsayapova, L I. Extraction of lighthydrocarbons from degassed oil under effect of CO₂//Geology, oilrecovery, physics and reservoir hydrodynamics/Works TatNIPIneft. Kazan:Tatarskoye Publishing House, 1973, Vol. No 22, p. 233, p. 236, p. 238;Vakhitov G G., Namiot A Yu., Skripka V. G. et al. Study of oildisplacement with nitrogen on reservoir model at pressures up to 70 MPa.//Neftianoye khoyastvo, 1985, No 1, p. 37/. During the process ofinjecting the working substance into the formation the concentration ofnitrogen and carbon dioxide in the hydrocarbon gas will also rise due toworking substance breakthrough into the production wells. For example,the carbon dioxide concentration in the hydrocarbon gas (Schedel R L inhis article uses the term <<(associated gas>>) can increase up to thelevels of 90% after a period of 6 months of carbon dioxideinjection/see: Schedel R L. EOR+CO₂=A gas processing challenge. //Oiland Gas Journal, 1982, Vol. 80, N 43, Oct. 25, p. 158/. Accordingly, thehydrocarbon gas quality will decrease because of considerable nitrogenand carbon dioxide presence, and the hydrocarbon gas ability to burnwill deteriorate.

[0061] That is, the increase in oil recovery and simultaneous increasein energy (and the working substance) generated by the power plant isachieved. Wherein, the increase of energy (and the working substance)production grows more intensively than the increase in the oil recovery.

[0062] Together with this, the hydrocarbon gas quality decreases becauseof nitrogen and carbon dioxide presence, and the hydrocarbon gas abilityto burn will deteriorate. Gas-condensate recovery from gas-condensatereservoirs goes in a similar manner. The gas-condensate recovery isincreased, and an amount of a gaseous mixture separated from therecovered fluid is increased. Wherein, the increase in the amount of thegaseous mixture is achieved also thanks to the gaseous hydrocarbonsextracted from the retrograde gas-condensate. Wherein, the quality ofthe gaseous mixture separated from the fluid decreases because ofconsiderable presence of inert gas, such as, nitrogen and carbondioxide.

[0063] Effective combustion of the separated gaseous mixture (all or apart of it) comprising hydrocarbon constituents and a considerableamount of inert gas (for example, such as, nitrogen and carbon dioxide)is realized thanks to the following: the separated gaseous mixture,intended for the combustion, and air, which is to be used as oxidant inthe combustion process, are mixed and a gas-air mixture resulting fromsaid mixing is compressed prior to said combustion, or the gas-airmixture is ignited during the compression (alternatively, the separatedgaseous mixture, intended for the combustion, and said air, which is tobe used as said oxidant in the combustion process, are compressed andthen are mixed to produce the gas-air mixture prior to said combustion,or the gas-air mixture is ignited, as soon as it is mixed). That is howprior to said combustion, the gas-air mixture, which is flammable andpressurized, is produced. This allows to widen the limits offlammability and, accordingly, to ensure combustion of the separatedgaseous mixture comprising hydrocarbon constituents and a considerableamount of nitrogen and carbon dioxide. For example, when pressure isincreased up to 1 MPa (that is, from 0.1 MPa to 1 MPa), the limits offlammability of the methane-air mixture widen to approximately twice asmuch in comparison with standard conditions, due to upper limit offlammability being increased./see: Lewis B., Elbe G. Combustion, flamesand explosions of gases —Moscow: Mir, 1968, p. 575/.

[0064] Thus, the increase in liquid hydrocarbons recovery andsimultaneous increase in the generated energy (and the workingsubstance) is achieved. Wherein, the increase of energy (and the workingsubstance) production grows more intensively than the increase in theliquid hydrocarbons recovery. Accordingly, thanks to the given property,the decrease of specific energy consumption (here, “energy” is theenergy received from exterior producers) to produce hydrocarbons fromhydrocarbon-bearing formations is achieved. For example, from anoil-bearing formation, or, for example, from a gas-condensate reservoir,or, from a natural gas reservoir, wherein natural gas is wet gas.

[0065] Schematic diagram shown on FIG. 1 illustrates the embodiments ofthe present invention.

[0066] The first embodiment of the invented method is realized in thefollowing manner. Hydrocarbon-containing fluid (hydrocarbon-containingfluid, usually comprises oil, gas and water, if the hydrocarbon-bearingformation is an oil-bearing formation; hydrocarbon-containing fluid,recovered from a gas-condensate reservoir, usually comprisesgas-condensate, gas and water) is recovered through production wells 1.We will make a special note regarding the use of the term “well”: wewill consider, that means for the well operation (for example, tubingstring), located within the limits of the well, is a part of the well(also, as in/see: Korotayev Yu P., Shirkovsky A I. Recovery,transportation and subterranean storage of gas.—Moscow: Nedra, 1984, p.60; Handbook on oil recovery/Edited by Gimatudinov Sh.K.—Moscow: Nedra,1974, p. 4031). Accordingly, the term swell” will include means for thewell operation (as a part of the well), necessary for its performance ina desired operating mode and for the well to fulfill its functions. Atleast a part of a gaseous mixture, comprising gaseous hydrocarbons, isseparated from the fluid. For example, a mixture of oil and gas (thatis, fluid in the form of a mixture of oil and gas) is recovered from anoil-bearing formation, and, at least a part of the gas is separated fromthe mixture of oil and gas. Said at least a part of the gaseous mixturemay be separated from the fluid, comprising a liquid component and thegaseous mixture, in a separator 2. Or, said at least a part of thegaseous mixture may be separated from the fluid in the production wells1. Then, said at least a part of the separated gaseous mixture is passed(for example, from the separator 2, or from an annular space of theproduction wells 1) into a power plant 4. Said at least a part of theseparated gaseous mixture is utilized as gaseous fuel in the power plant4, wherein said at least a part of the separated gaseous mixture iscombusted. Said at least a part of the separated gaseous mixture andair, to be used as oxidant, are mixed and a gas-air mixture resultingfrom said mixing is compressed prior to said combustion, or the gas-airmixture is ignited during said compression. We will make a special noteregarding the use of the term “gas-air mixture”. The term “gas-airmixture” denotes a composition, comprising gaseous fuel (for example, atleast a part of a separated gaseous mixture) and air, which is to beused as oxidant in combustion process. That is, also, as in/see:Isserlin A. S. The basics of gaseous fuel combustion. Moscow: Nedra,1987, p. 60; Yefimov S. I., Ivaschenko N. A., Ivin V. I. et al: Internalcombustion engines: Systems of piston type and combination type engines.Moscow: Mashinostroyeniye, 1985, p. 223/. Mixing of the air with said atleast a part of the separated gaseous mixture may be realized in thepower plant 4, or in other means (not shown). Said at least a part ofthe separated gaseous mixture and/or the air, which is to be used as theoxidant, may be compressed prior to forming of the gas-air mixture toenhance the subsequent forming of the gas-air mixture. The gas-airmixture may be heated (for example, in the power plant 4), or said atleast a part of the separated gaseous mixture may be heated prior toforming of the gas-air mixture, so that to avoid moisture condensationduring said compression of the gas-air mixture. Pressure of thepressurized gas-air mixture may be established according to thecomposition of said at least a part of the separated gaseous mixture(according to the separated gaseous mixture methane number). Saidcompression of the gas-air mixture may be realized in a device containedin the power plant 4, or in another device, for example, in a compressor(not shown), which is not contained in the power plant 4. For example,to produce some mechanical energy, the power plant 4 may comprise a gasengine or a gas-diesel engine (any of them may be used to drive anelectrical generator and/or an injection device to inject the workingsubstance or water into the formation, for example, a compressor, or apump), in any of them said at least a part of the separated gaseousmixture and the air are mixed and the gas-air mixture resulting fromsaid mixing is compressed prior to said combustion of said at least apart of the separated gaseous mixture, which is used as the gaseousfuel, with the air, which is used as the oxidant. Depending on acomposition of the gas-air mixture and the type of the power plant 4,said combustion of the gas-air mixture is started after saidcompression, or during said compression. For example, in a gas engine,having spark ignition system, the moment of ignition of a gas-airmixture is determined by choosing a corresponding meaning of sparkignition advance. Ignition of the gas-air mixture (after itscompression, or during its compression) may be realized by injectingother combustible substances into it (for example, usually, in agas-diesel engine, when the compression stroke approaches its end, asmall quantity of liquid fuel is injected into a gas-air mixture). Whencombusting said at least a part of the separated gaseous mixture in thepower plant 4, the desired ratio of said at least a part of theseparated gaseous mixture and the air may be maintained, for example,the gas-air mixture may comprise the air in the amount which istheoretically necessary for oxidizing combustible constituents of thegas-air mixture, or the gas-air mixture may comprise more of the air,than it is theoretically necessary for oxidizing the combustibleconstituents of the gas-air mixture (for example, to ensure the completecombustion of combustible constituents of said at least a part of theseparated gaseous mixture). The gas-air mixture may contain less of theair, than it is theoretically necessary for oxidizing the combustibleconstituents of the gas-air mixture, when it is necessary to achievelower oxygen ratio in the products of combustion. The separated gaseousmixture may comprise heavy hydrocarbons. In connection with this, saidat least a part of the separated gaseous mixture (or, the gas-airmixture) and/or the air, which is to be used as oxidant, may be mixedwith a part of exhaust gases of the power plant 4 in the power plant 4,or in a unit 3 for preparing the separated gaseous mixture (we will callthe unit 3 “the preparation unit 3”), to enhance the detonationcharacteristic of said at least a part of the separated gaseous mixture,which is to be utilized as the gaseous fuel. For example, it may berealized during the beginning phase of working substance injection (whencarbon dioxide and nitrogen concentration in said at least a part of theseparated gaseous mixture is not very significant). The exhaust gases ofthe power plant 4 comprise carbon dioxide and nitrogen. And, as we know,the methane number of gaseous fuel increases with the increase of thenitrogen and carbon dioxide concentration in the gaseous fuel(accordingly, the detonation characteristic of the gaseous fuel isenhanced). Thus, if the separated gaseous mixture comprises the heavyhydrocarbons, then said at least a part of the separated gaseous mire(or the gas-air mixture) and/or the air, which is to be used as theoxidant, may be mixed with the part of the exhaust gases. Consequently,in this case the gas-air mixture comprises said at least a part of theseparated gaseous mixture, the air, which is to be used as the oxidant,and the part of the exhaust gases of the power plant.

[0067] Alternatively, said at least a part of the separated gaseousmixture may be directed into the preparation unit 3, where said at leasta part of the separated gaseous mixture is prepared for combustion inthe power plant 4. Sulfur containing substances, solid particles,moisture, other contaminants and heavy hydrocarbons are removed fromsaid at least a part of the separated gaseous mixture to decrease theirconcentration down to the desired level in accordance with therequirements demanded from the composition of mixtures intended forcombustion in the power plant 4. Said at least a part of the separatedgaseous mixture may be heated in the preparation unit 3 to avoidmoisture condensation. Also, the gas-air mixture may be heated prior tocompression. In the preparation unit 3 (if there is an excessive amountof nitrogen and/or carbon dioxide in the gaseous mixture separated fromthe produced fluid) nitrogen and/or carbon dioxide may be separated fromsaid at least a part of the separated gaseous fluid.

[0068] Then, the nitrogen and/or the carbon dioxide is passed into a gasseparation unit 9 (or to an outlet of the gas separation unit 9) or toan inlet of an injection unit 10 (not shown), to be injected into theformation. Also, a continuous supply of said at least a part of theseparated gaseous mixture into the power plant 4 may be provided byusing the preparation unit 3. The power plant 4 may comprise, forexample, a gas engine (instead of which a gas-diesel engine or somethingcomparable may be used) and an electric generator, the shafts of whichare connected via mechanical drive means. The power plant 4 maycomprise, for example, a cooling system. Also, a waste-heat boiler 7 maybe connected to the power plant 4 (or the power plant 4 may comprise awaste-heat boiler 7). Heat energy produced in the power plant 4 istransferred to heat-carriers or a heat-carrier (for example, to waterand/or gas, which is to be injected) when the heat-carrier (or theheat-carriers) passes through a heat exchanger 6 of the cooling systemof the power plant 4 and/or through the waste-heat boiler 7. And, then,said heat energy is transferred further with the help of theheat-carriers for utilization. Also, the power plant 4 may comprisemeans for regulating its performance modes, when the composition and/orthe amount of said at least a part of the separated gaseous mixturedirected for combustion into the power plant 4, is changed. Theelectrical energy generated by the power plant 4 is used to supplyoilfield equipment, and may be generated into an electrical network and,if it becomes necessary, may be used for an additional heating of waterand the working substance in electrical heaters 11 and 13.

[0069] Carbon dioxide and nitrogen are a major part of products ofcombustion of said at least a part of the separated gaseous mixture inthe power plant 4. Concentration of carbon dioxide and nitrogen in dryexhaust gases of the power plant 4 may be as much as 90% and even more.

[0070] Because of this, at least a part of exhaust gases is used forinjection into the hydrocarbon-bearing formation. That is, it is ensuredthat said at least a part of the separated gaseous mixture is combustedin the power plant 4 and energy (for example, electrical and/or heat) isgenerated in the power plant 4, and the exhaust gases, resulting fromsaid combustion and comprising nitrogen and carbon dioxide as theircomponents, are discharged from the power plant 4, and at least a partof the exhaust gases is injected into the hydrocarbon-bearing formation.A temperature of the exhaust gases of the power plant 4 may be about350-400° C. In connection with this, the exhaust gases, after beingproduced in the power plant 4, may be directed into the waste-heatboiler 7, where they transfer their heat energy to other heat-carriers.Also, prior to injection, when it is necessary, said at least a part ofthe exhaust gases is treated for removal of corrosive substances(oxygen, nitrogen oxides and some others), mechanical contaminants andmoisture in an exhaust gas purification unit 8. Dehydration of theexhaust gases may be performed in the following manner: said at least apart of the exhaust gases may be compressed prior to dehydration, afterwhich, moisture is removed from said exhaust gases. Further, the workingsubstance composition (wherein the working substance is a gas comprisingsaid at least a part of the exhaust gases) is established according tothe geological-and-physical characteristic and the development stage ofthe formation. Said at least a part of the exhaust gases may be directedinto the gas separation unit 9. Specifically, the working substancetreatment to the desirable composition may be performed by reducing theconcentration of nitrogen in the exhaust gases in the gas separationunit 9. Also, the treatment of the working substance to the desirablecomposition may be performed by introducing certain constituents intoit. The working substance is injected into the formation throughinjection wells 15 by means of the injection unit 10. The workingsubstance is compressed prior to injection. Compression is realized inthe injection unit 10, which may comprise a compressor (which is driven,for example, with the help of mechanical or electrical energy generatedby the power plant 4). Distribution of the working substance between theinjection wells 15 may be realized in a distribution unit 12.Temperature of the working substance may be increased, after thecompression of the working substance in the unit 10 and prior to theworking substance being injected into the injection wells 15. For thisthe working substance may be directed into the heat exchanger 6 and/orthe waste-heat boiler 7. A certain temperature of the working substanceis established in the heat exchanger 6 and/or in the waste-heat boiler7, specifically, considering the geological-and-physical characteristicand the development stage of the formation. Additionally, the workingsubstance may be heated in an electrical heater 11. An order of theworking substance's passing through the heat exchanger 6 and thewaste-heat boiler 7 is set, depending on the design, temperature andinjection pressure meanings. When it is necessary, the working substancemay be directed from the distribution unit 12 into the production wells1, to treat a zone of the formation in the vicinity of the wells 1.

[0071] Also, water may be injected into the formation through theinjection wells 15. For this, the water from water treatment plant 5 ispassed into pumps 16. The water is fed by the pumps 16 into theinjection wells 15. The water may be distributed between the injectionwells 15 through a distribution unit 14. If it is necessary, thetemperature of the water may be increased, the water is heated in theheat exchanger 6 and/or in the waste-heat boiler 7, according to thegeological-and-physical characteristic and the development stage of theformation.

[0072] Additionally, the water may be heated in an electrical heater 13.The water may be injected into one injection well or into a plurality ofwells simultaneously with the working substance (for example, whenmixing the water with the working substance in an injection well), orone after another. Alternatively, a group of injection wells is used toinject the working substance, and another group of injection wells isused to inject water.

[0073] Example: electrical energy consumed to realize oil recovery andother technological processes performed at an oil-field (withoutconsidering the electrical energy consumed to realize gas injection) isequal to approximately 163-192 kWh per one ton of produced oil/see:Aroutyunov A. I., Louzin V. I., Maximov V. P. et al. New trends in useof hydrocarbon gas //Ekonomika i organizatsiia promishlennogoproizvodstva, 1980, No 10 (76), p. 67, p. 68, p. 70/. A gas factor isequal to 100 m³/t; and 60% of the gaseous mixture is separated fromoil-containing fluid during the first stage of separation. The gaseousmixture, separated from the fluid, is combusted with air, which is usedas oxidant, in a power plant (or power plants), wherein the gaseousmixture and the air are mixed to produce a gas-air mixture, which iscompressed prior to said combustion (pressure of the gas-air mixture atthe moment of ignition is equal to 1 MPa). The working substance(exhaust gases of the power plant or the power plants) is injected intothe formation through injection wells. The electrical energy consumed torealize the injection of the working substance is equal to 80 kWh perone ton of produced oil. In the beginning of the working substanceinjection, gaseous hydrocarbons constitute approximately 100% of theseparated from the produced fluid gaseous mixture. The lower heatingvalue of the gaseous hydrocarbons (75% of mass of gaseous hydrocarbonsmolecules is carbon) equals to Q_(H)≈36×10⁶ Joule/m³; the upper limitand the lower limit of flammability of the gas-air mixture (whenpressure is equal to 1 MPa, and temperature is equal to 20° C.) will berespectively about 23.5% and about 4.49%/see: Lewis B., Elbe G.Combustion, flames and explosions of gases.—Moscow: Mir, 1968, p. 575/.When supplying 300 m³/h of the gaseous mixture (which is ensured by oilproduction of 120 t/day) into the power plant in the beginning of theworking substance injection into the formation, useful power, given bythe generator of the power plant to users, will be P≈900 kW, heatenergy, given to heat carriers (for example, water) will be Q≈1.29×10⁹cal/h. Wherein, nitrogen and carbon dioxide (contained as components ofthe exhaust gases of the power plant) are discharged from the powerplant in the amount of VP=2556 m³/h (including, carbon dioxide more than11%). Thus, with the given conditions—in the beginning of the workingsubstance injection, when 1 ton of oil is produced, approximately 180kWh of electrical energy may be generated by the power plant (where theseparated from the fluid gaseous mixture is utilized as gaseous fuel).Accordingly, the specific energy consumption (here, “energy” is theenergy received from exterior producers) to realize the oil recovery andother technological processes performed at an oil-field will be not morethan 92 kWh per 1 ton of recovered oil.

[0074] With the daily oil production increased by 100/, the supply ofthe gaseous mixture into the power plant will also increase (which isinterrelated with the increase in oil production and is caused by theincrease of the gas factor, which is realized also due to the ability ofthe working substance to extract gaseous hydrocarbons fromoil-containing fluid present in the formation), and it will be about 800m³/h (this will also include about 400 m³/h of the gaseoushydrocarbons). Accordingly, the gaseous mixture comprises 50% of inertgas (which consists of 90% of nitrogen and 10% of carbon dioxide) and50% of gaseous hydrocarbons (the lower heating value of the gaseoushydrocarbons is Q_(H)≈36×10⁶ Joule/m³, wherein 75% of mass of gaseoushydrocarbons molecules is carbon). When supplying said volume of thegaseous mixture with said composition into the power plant, the usefulpower, given by the generator of the power plant to users, will beP≈1200 kW, heat energy, given to heat carriers (for example, water) willbe Q≈1.72×10⁹ cal/h. Wherein, nitrogen and carbon dioxide (contained ascomponents of the exhaust gases of the power plant) are discharged fromthe power plant in the amount of V_(p)≈3808 m³/h (including, carbondioxide more than 11%). The upper limit and the lower limit offlammability of the gas-air mixture (when pressure is equal to 1 MPa,temperature is equal to 20° C.) will be respectively about 37.4% andabout 8.61% (as far as, the combustible constituent is concerned, therespective values will be about 18.7% and about 4.05%). Thus, with thegiven conditions, when 1 ton of oil is produced, approximately 218 kWhof electrical energy may be generated by the power plant (where theseparated from the fluid gaseous mixture is utilized as gaseous fuel).Accordingly, the specific energy consumption (here, “energy” is theenergy received from exterior producers) to realize the oil recovery andother technological processes performed at an oil-field will be not morethan 54 kWh per 1 ton of recovered oil.

[0075] The second embodiment of the invented method is realized in thefollowing manner. At least a part of a gaseous mixture, comprisinggaseous hydrocarbons, is separated from hydrocarbon-containing fluid(hydrocarbon-containing fluid, usually comprises oil, gas and water, ifthe hydrocarbon-bearing formation is an oil-bearing formation;hydrocarbon-containing fluid, recovered from a gas-condensate reservoirusually comprises gas-condensate, gas and water), recovered throughproduction well 1. For example, a mixture of oil and gas (that is, fluidin the form of a mixture of oil and gas) is recovered from anoil-bearing formation, and, at least a part of the gas is separated fromthe mixture of oil and gas. Said at least a part of the gaseous mixturemay be separated from the fluid, comprising a liquid component and thegaseous mixture, in a separator 2, or at least a part of the gaseousmixture may be separated from the fluid in the production wells 1. Then,said at least a part of the separated gaseous mixture is passed (forexample, from the separator 2, or from an annular space of theproduction wells 1) into a power plant 4. Said at least a part of theseparated gaseous mixture is utilized as gaseous fuel in the power plant4, wherein said at least a part of the separated gaseous mixture iscombusted. Said at least a part of the separated gaseous mixture andair, which is to be used as oxidant, are compressed and then mixed toproduce a gas-air mixture prior to said combustion, or the gas-airmixture is ignited, as soon as it is mixed. Pressure of the pressurizedair, which is to be used as the oxidant, and pressure of the pressurizedsaid at least a part of the gaseous mixture may be established accordingto the composition of said at least a part of the separated gaseousmixture (according to the separated gaseous mixture methane number).Said compression may be realized in a device contained in the powerplant 4, or in another device, for example, in a compressor (not shown),which is not contained in the power plant 4. For example, to producesome mechanical energy, the power plant 4 may comprise a gas turbineengine (which may be used to drive an electrical generator and/or aninjection device to inject the working substance or water into theformation, for example, a compressor, or a pump), in which said at leasta part of the separated gaseous mixture and the air are compressed andthen mixed to produce the gas-air mixture prior to said combustion ofsaid at least a part of the separated gaseous mixture, which is used asthe gaseous fuel, with the air, which is used as the oxidant. We willmake a special note regarding the use of the term “gas turbine engine”,which is used here and after, according to the terminology acceptedin/see: Polytechemical dictionary/edited by: A. Yu. Ishlinsky. Moscow:Sovietskaya encyclopedia.—1989, p. 107/. In accordance with thisterminology, the term “gas turbine engine” may also be used to cover theconcept of “gas turbine plant”, which occasionally is used in thetechnical literature when it comes to describing engines with gasturbines, designed to drive stationary machines and devices. Dependingon a composition of the gas-air mixture and the type of the power plant4, ignition of the gas-air mixture is realized by way of injecting otherflammable substances into it. When combusting said at least a part ofthe separated gaseous mixture in the power plant 4, the desired ratio ofsaid at least a part of the separated gaseous mixture and the air may bemaintained, for example, the gas-air mixture may comprise the air in theamount which is theoretically necessary for oxidizing the combustibleconstituents of the gas-air mixture, or the gas-air mixture may comprisemore of the air, than it is theoretically necessary for oxidizing thecombustible constituents of the gas-air mixture (for example, to ensurethe complete combustion of combustible constituents of said at least apart of the separated gaseous mixture). The gas-air mixture may containless of the air, than it is theoretically necessary for oxidizing thecombustible constituents of the gas-air mixture, when it is necessary toachieve lower oxygen ratio in the products of combustion. The separatedgaseous mixture may comprise heavy hydrocarbons. In connection withthis, said at least a part of the separated gaseous mixture and/or theair, which is to be used as the oxidant, (or, the gas-air mixture) maybe mixed with a part of exhaust gases of the power plant 4 in the powerplant 4, or in a unit 3 for preparing the separated gaseous mixture (wewill call the unit 3 “the preparation unit 3”), to enhance thedetonation characteristic of said at least a part of the separatedgaseous mixture, which is to be utilized as gaseous fuel. For example,it may be realized during the beginning phase of working substanceinjection (when carbon dioxide and nitrogen concentration in said atleast a part of the separated gaseous mixture is not very significant).The exhaust gases of the power plant 4 comprise carbon dioxide andnitrogen. And, as we know, the methane number of gaseous fuel increaseswith the increase of the nitrogen and carbon dioxide concentration inthe gaseous fuel (accordingly, the detonation characteristic of thegaseous fuel is enhanced). Thus, if the separated gaseous mixturecomprises the heavy hydrocarbons, then said at least a part of theseparated gaseous mixture (or the gas-air mixture) and/or the air may bemixed with the part of the exhaust gases. Consequently, in this case thegas-air mixture comprises said at least a part of the separated gaseousmixture, the air, which is to be used as the oxidant, and the part ofthe exhaust gases of the power plant.

[0076] Alternatively, said at least a part of the separated gaseousmixture may be directed into the preparation unit 3, where it isprepared for combustion in the power plant 4. Sulfur containingsubstances, solid particles, moisture, other constituents and heavyhydrocarbons are removed from said at least a part of the separatedgaseous mixture to decrease their concentration down to the desiredlevel in accordance with the requirements demanded from the compositionof mixtures intended for combustion in the power plant 4. Said at leasta part of the separated gaseous mixture may be heated in the preparationunit 3 to avoid moisture condensation. In the preparation unit 3 (ifthere is an excessive amount of nitrogen and/or carbon dioxide in thegaseous mixture separated from the produced fluid) nitrogen and/orcarbon dioxide may be separated from said at least a part of theseparated gaseous mixture. Then, the nitrogen and/or the carbon dioxideis passed into a gas separation unit 9 (or to an outlet of the gasseparation unit 9) or to an inlet of an injection unit 10 (not shown) tobe injected into the formation. Also, a continuous supply of said atleast a part of the separated gaseous mixture into the power plant 4 maybe provided by using the preparation unit 3. The power plant 4 maycomprise, for example, a gas turbine engine and an electric generator,the shafts of which are connected via mechanical drive means. The powerplant 4 may comprise, for example, a cooling system. Also, a waste-heatboiler 7 may be connected to the power plant 4 (or the power plant 4 maycomprise a waste-heat boiler 7). Heat energy produced in the power plant4 is transferred to heat-carriers or a heat-carrier (for example, towater and/or gas, which is to be injected) when the heat-carrier (or theheat-carriers) passes through a heat exchanger 6 of the cooling systemof the power plant 4 and/or through the waste-heat boiler 7. And, then,said heat energy is transferred further with the help of theheat-carriers for utilization. Also, the power plant 4 may comprisemeans for regulating its performance modes, when the composition and/orthe amount of said at least a part of the separated gaseous mixturedirected for combustion into the power plant 4, is changed. Theelectrical energy generated by the power plant 4 is used to supplyoilfield equipment, and may be generated into an electrical network and,if it becomes necessary, may be used for an additional heating of waterand the world substance in electrical heaters 11 and 13.

[0077] Carbon dioxide and nitrogen are a major part of products ofcombustion of said at least a part of the separated gaseous mixture inthe power plant 4. Concentration of carbon dioxide and nitrogen in dryexhaust gases of the power plant 4 may be as much as 90% and even more.Because of this, at least a part of exhaust gases is used for injectioninto the hydrocarbon-bearing formation. That is, it is ensured that saidat least a part of the separated gaseous mixture is combusted in thepower plant 4 and energy (for example, electrical and/or heat) isgenerated in the power plant 4, and the exhaust gases (comprisingnitrogen and carbon dioxide as their components) are discharged from thepower plant 4, and at least a part of the exhaust gases is injected intothe hydrocarbon-bearing formation. A temperature of the exhaust gases ofthe power plant 4 may be about 350-400° C. In connection with this, theexhaust gases, after being produced in the power plant 4, may bedirected into the waste-heat boiler 7, where they transfer their heatenergy to other heat-carriers. Also, prior to injection, when it isnecessary, said at least a part of the exhaust gases is treated forremoval of corrosive substances (oxygen, nitrogen oxides and someothers), mechanical contaminants and moisture in an exhaust gaspurification unit 8. Dehydration of the exhaust gases may be performedin the following manner: said at least a part of the exhaust gases maybe compressed prior to dehydration, after which, moisture is removedfrom said exhaust gases. Further, the working substance composition(wherein the working substance is a gas comprising said at least a partof the exhaust gases) is established according to thegeological-and-physical characteristic and the development stage of theformation. Said at least a part of the exhaust gases may be directedinto the gas separation unit 9. Specifically, the working substancetreatment to the desirable composition may be performed by reducing theconcentration of nitrogen in the exhaust gases in the gas separationunit 9. Also, the treatment of the working substance to the desirablecomposition may be performed by introducing certain constituents intoit. The working substance is injected into the formation throughinjection wells 15 by means of the injection unit 10. The workingsubstance is compressed prior to injection. Compression is realized inthe injection unit 10, which may comprise a compressor (which is driven,for example, with the help of mechanical or electrical energy generatedby the power plant 4). Distribution of the working substance between theinjection wells 15 may be realized in a distribution unit 12.Temperature of the working substance may be increased, after thecompression of the working substance in the unit 10 and prior to theworking substance being injected into the injection wells 15. For thisthe working substance may be directed into the heat exchanger 6 and/orthe waste-heat boiler 7. A certain temperature of the working substanceis established in the heat exchanger 6 and/or in the waste-heat boiler7, specifically, considering the geological-and-physical characteristicand the development stage of the formation. Additionally, the workingsubstance may be heated in an electrical heater 11. An order of theworking substance's passing through the heat exchanger 6 and thewaste-heat boiler 7 is set, depending on the design, temperature andinjection pressure meanings. When it is necessary, the working substancemay be directed from the distribution unit 12 into the production wells1, to treat a zone of the formation in the vicinity of the wells 1.

[0078] Also, water may be injected into the formation through theinjection wells 15. For this, the water from water treatment plant 5 ispassed into pumps 16. The water is fed by the pumps 16 into theinjection wells 15. The water may be distributed between the injectionwells 15 through a distribution unit 14. If it is necessary, thetemperature of the water may be increased, the water is heated in theheat exchanger 6 and/or in the waste-heat boiler 7, according to thegeological-and-physical characteristic and the development stage of theformation. Additionally, the water may be heated in an electrical heater13. The water may be injected into one injection well or into aplurality of wells simultaneously with the working substance (forexample, when mixing the water with the working substance in aninjection well), or one after another. Alternatively, a group ofinjection wells is used to inject the working substance, and anothergroup of injection wells is used to inject water.

[0079] Example: electrical energy consumed to realize oil recovery andother technological processes performed at an oil-field (withoutconsidering the electrical energy consumed to realize gas injection) isequal to approximately 163-192 kWh per one ton of produced oil/see:Aroutyunov A. I., Louzin V. I., Maximov V. P. et al. New trends in useof hydrocarbon gas //Ekonomika i organizatsiia promishlennogoproizvodstva, 1980, No 10 (76), p. 67, p. 68, p. 70/. A gas factor isequal to 100 m³/t; 60% of the gaseous mixture is separated fromoil-containing fluid during the first stage of separation. The gaseousmixture, separated from the fluid, is combusted with air, which is usedas oxidant, in a power plant (or power plants), wherein the gaseousmixture and the air are compressed and then mixed to produce a gas-airmixture prior to said combustion (pressure of the gas-air mixture at themoment of ignition is equal to 1 MPa). The working substance (exhaustgases of the power plant or the power plants) is injected into theformation through injection wells. The electrical energy consumed torealize the injection of the working substance is equal to 80 kWh perone ton of produced oil. In the beginning of the working substanceinjection, gaseous hydrocarbons constitute approximately 100% of theseparated from the produced fluid gaseous mixture. The lower heatingvalue of the gaseous hydrocarbons (75% of mass of gaseous hydrocarbonsmolecules is carbon) equals to Q_(H)≈36×10⁶ Joule/m³; the upper limitand the lower limit of flammability of the gas-air mixture (whenpressure is equal to 1 MPa, and temperature is equal to 20° C.) will berespectively about 23.5% and about 4.49%/see: Lewis B., Elbe G.Combustion, flames and explosions of gases.—Moscow: Mir, 1968, p. 575/.When supplying 300 m³/h of the gaseous mixture (which is ensured by oilproduction of 120 t/day) into the power plant in the beginning of theworking substance injection into the formation, useful power, given bythe generator of the power plant to users, will be P≈900 kW, heatenergy, given to heat carriers (for example, water) will be Q≈1.29×10⁹cal/h. Wherein, nitrogen and carbon dioxide (contained as components ofthe exhaust gases of the power plant) are discharged from the powerplant in the amount of V_(p=)2556 m³/h (including, carbon dioxide morethan 11%). Thus, with the given conditions—in the beginning of theworking substance injection, when 1 ton of oil is produced,approximately 180 kWh of electrical energy may be generated by the powerplant (where the separated from the fluid gaseous mixture is utilized asgaseous fuel). Accordingly, the specific energy consumption (here,“energy” is the energy received from exterior producers) to realize theoil recovery and other technological processes performed at an oil-fieldwill be not more than 92 kWh per 1 ton of recovered oil.

[0080] With the daily oil production increased by 10%, the supply of thegaseous mixture into the power plant will also increase (which isinterrelated with the increase in oil production and is caused by theincrease of the gas factor, which is realized also due to the ability ofthe working substance to extract gaseous hydrocarbons fromoil-containing fluid present in the formation), and it will be about 800m³/h (this will also include about 400 m³/h of gaseous hydrocarbons).Accordingly, the gaseous mixture comprises 50% of inert gas (whichconsists of 90% of nitrogen and 10% of carbon dioxide) and 50% ofgaseous hydrocarbons (the lower heating value of the gaseoushydrocarbons is Q_(H=)≈36×10⁶ Joule/m³, wherein 75% of mass of gaseoushydrocarbons molecules is carbon). When supplying said volume of thegaseous mixture with said composition into the power plant, the usefulpower, given by the generator of the power plant to users, will beP≈1200 kW, heat energy, given to heat carriers (for example, water) willbe Q_(H)1.72×10⁹ cal/h. Wherein, nitrogen and carbon dioxide (containedas components of the exhaust gases of the power plant) are dischargedfrom the power plant in the amount of V_(p)≅3808 m³/m³h (including,carbon dioxide more than 11%). The upper limit and the lower limit offlammability of the gas-air mixture (when pressure is equal to 1 MPa,and temperature is equal to 20° C.) will be respectively about 37.4% andabout 8.61% (as far as, the combustible constituent is concerned, therespective values will be about 18.7% and about 4.05%). Thus, with thegiven conditions, when 1 ton of oil is produced, approximately 218 kWhof electrical energy may be generated by the power plant (where theseparated from the fluid gaseous mixture is utilized as gaseous fuel).Accordingly, the specific energy consumption (here, “energy” is theenergy received from exterior producers) to realize the oil recovery andother technological processes performed at an oil-field will be not morethan 54 kWh per 1 ton of recovered oil.

[0081] The essence of the method being offered is in the following. Asit has been stated before, when a working substance is injected into ahydrocarbon-bearing formation, a volume of liquid hydrocarbons,recovered from the formation, increases. Also, a volume of a gaseousmixture separated from a hydrocarbon-containing fluid will increase.Accordingly, this will allow to increase the separated gaseous mixturesupply into the power plant. This will provide for a possibility toincrease an amount of energy generated by the power plant and an amountof the produced working substance. The increase of the amount of theenergy generated by the power plant and the increase of the amount ofthe produced working substance not only corresponds with the increase ofthe liquid hydrocarbons recovery, but it is also conditioned by theincrease of the gas factor, which is realized also due to gaseoushydrocarbons extraction from a hydrocarbon-containing fluid present inthe formation, and, wherein during the process of injecting the workingsubstance into the formation the concentration of nitrogen and carbondioxide in the separated gaseous mixture will also rise due to workingsubstance breakthrough into the production wells.

[0082] That is, the increase in the liquid hydrocarbons recovery andsimultaneous increase in the energy (and the working substance)generated by the power plant is achieved. Wherein, the increase ofenergy (and the working substance) production grows more intensivelythan the increase in the oil recovery. Together with this, the separatedgaseous mixture quality decreases because of nitrogen and carbon dioxidepresence, and the separated gaseous mixture ability to burn willdeteriorate. For example, at the Budafa oilfield block, when injectinggas, comprising about 80% of carbon dioxide, and water, one afteranother, after 15 months of injecting, the separated from oil-containingfluid gas comprised about 60% of carbon dioxide/see: Balint V., Ban A.,Doleshal Sh. et al: Use of carbon dioxide in oil recovery.—Moscow:Nedra, 1977, p.223, p. 224/. As it has been stated earlier, the carbondioxide concentration in the hydrocarbon gas (Schedel R. L in hisarticle uses the term <<associated gas>>) can increase up to the levelsof 90% after a period of 6 months of carbon dioxide injection/see:Schedel R. L. EOR+CO₂=A gas processing challenge. //Oil and Gas Journal1982, Vol. 80, N 43, Oct. 25, p. 158/. Having in mind, that nitrogen hasa lower level of solubility than carbon dioxide in ahydrocarbon-containing fluid, the above statement will be true wheninjecting nitrogen or nitrogen and carbon dioxide mixture into theformation.

[0083] Thus, nitrogen and carbon dioxide injection into ahydrocarbon-bearing formation is inseparably connected with aconsiderable increase of a gas factor (including, the increase of theamount of the produced gaseous hydrocarbons due to the gaseoushydrocarbons extraction from hydrocarbon-containing fluid present in theformation), which goes along with a considerable increase of nitrogenand carbon dioxide concentration in a gaseous mixture separated from theproduced fluid. Accordingly, the separated gaseous mixture qualitydecreases together with its ability to burn.

[0084] Effective combustion of the separated gaseous mixture comprisinghydrocarbon constituents and a considerable amount of inert gas (forexample, such as, nitrogen and carbon dioxide) is realized thanks to thefollowing: the separated gaseous mixture and air, which is to be used asoxidant in the combustion process, are mixed and a gas-air mixtureresulting from said mixing is compressed prior to said combustion, orthe gas-air mixture is ignited during said compression (alternately, theseparated gaseous mixture and said air, which is to be used as saidoxidant in the combustion process, are compressed and then are mixed toproduce the gas-air mixture prior to said combustion, or the gas-airmixture is ignited, as soon as it is mixed). That is how prior to saidcombustion, the gas-air mixture, which is flammable and pressurized, isproduced. This allows to widen the limits of flammability and,accordingly, to ensure combustion of the separated gaseous mixturecomprising hydrocarbon constituents and a considerable amount ofnitrogen and carbon dioxide. For example, when a mixture, consisting of50% of methane and 50% of inert gas (said inert gas contains 90% ofnitrogen and 10% of carbon dioxide), is combusted with atmospheric air,the upper limit and the lower limit of flammability of the gas-airmixture (when, pressure is equal to 1 MPa, and temperature is equal to20° C.), comprising said mixture and the air, will be respectively 37.4%and 8.61% (as far as, the combustible constituent is concerned, therespective values will be 18.7% and 4.05%). That is, combustion of saidmixture may be realized in a gas engine with the compression ratio valueof 10. The same result may be achieved, when a mixture, consisting of10% of methane and 90% of inert gas (said inert gas contains 90% ofnitrogen and 10% of carbon dioxide), is combusted with atmospheric air,the upper limit and the lower limit of flammability of the gas-airmixture (when, pressure is equal to 1 MPa, and temperature is equal to20° C.), comprising said mixture and the air, will be respectively 74.9%and 32.03% (as far as, the combustible constituent is concerned, therespective values will be 7.49% and 3.203%). The calculations were doneusing the data from following works: /see: Lewis B., Elbe G. Combustion,flames and explosions of gases.—Moscow: Mir, 1968, p. 575; Isserlin A.S. The basics of gaseous fuel combustion. Moscow: Nedra, 1987, p.p.69-71/.

[0085] Thus, the increase in liquid hydrocarbons recovery andsimultaneous increase in the produced energy (and the working substance)is achieved. Wherein, the increase of energy (and the working substance)production grows more intensively than the increase in the liquidhydrocarbons recovery. Accordingly, thanks to the given property, thedecrease of specific energy consumption (here, “energy” is the energyreceived from exterior producers) to produce hydrocarbons from thehydrocarbon-bearing formations is achieved. For example, from anoil-bearing formation, or, from an oil-bearing formation with a gas cap,or, for example, from a gas-condensate reservoir, or, from a natural gasreservoir, where natural gas is wet gas.

[0086] Also, the present invention will provide an environmentally saferhydrocarbons production process from a hydrocarbon-bearing formation dueto carbon dioxide being injected into the formation instead of beingreleased into the atmosphere.

[0087] For the execution of the described above method the system isoffered.

[0088] Systems for viscous oil recovery are well known. One of thesystems comprises a slot-jet compressor in fluid communication with asteam generator. Steam and flue gas, produced by the steam generator,are mixed in the slot-jet compressor to produce a steam-gas mixture. Thesteam-gas mixture is injected into the oil-bearing formation through aninjection well/see: RU patent No 2046933 C1, cl. E21B 43/24, publishedon 27 Oct. 1995/. However, there is a problem of supplying surfaceoilfield equipment with energy.

[0089] The closest in its technical essence and the achieved result,will be a system, comprising a power plant with an electrical generatorand an exhaust gas outlet. The power plant converts fuel energy intoheat energy, a part of the heat energy is converted into mechanicalenergy, which is converted into electrical energy (using an electricalgenerator). The system also comprises an injection device with at leastone of its outlets being in fluid communication with at least oneinjection well. The power plant is adapted to be in fluid communication(through a separator) with at least one production well/see: USSRInventors Certificate No 21729300 A3, cl. E21B 43/24, published on 23Apr. 1992/. This system is known for its high fuel-energy consumption inthe power plant (which consists of a high-temperature reactor, a closedhelium contour, two steam generators, a reaction furnace, a gas-blower,a heater, a steam turbine mechanically connected with an electricalgenerator) during the process of influencing the formation, which isexecuted by steam being injected into the formation by the injectiondevice (which is represented by a pump with a steam converter).Accordingly, the increase in production of hydrocarbons is obtained bysignificant energy consumption.

[0090] The objects of this invention are: to increase the hydrocarbonsrecovery, while maintaining a high rate of energy effectiveness of thehydrocarbons production process from a hydrocarbon-bearing formation,and, besides, to increase the amount of produced energy, and to providean environmentally safer hydrocarbons production process from thehydrocarbon-bearing formation.

[0091] Technical result according to the first embodiment of theinvented system, comprising:

[0092] a power plant with an electrical generator, the power planthaving an exhaust gas outlet and being adapted to be in fluidcommunication with at least one production well, an injection meanshaving an outlet adapted to be in fluid communication with at least oneinjection well,

[0093] is achieved due to the fact, that

[0094] the power plant comprises a gas engine, or a gas turbine engineor a gas-diesel engine, any of said engines is adapted to dischargeexhaust gases, which comprise nitrogen and carbon dioxide as theircomponents,

[0095] the electrical generator being connected via mechanical drivemeans with the gas engine, or the gas turbine engine, or the gas-dieselengine,

[0096] and the exhaust gas outlet being in fluid communication with aninlet of said injection means;

[0097] it further comprises a separator, the power plant being inadditional fluid communication with said production well through theseparator;

[0098] the power plant has more than one exhaust gas outlet;

[0099] said injection means comprises a compressor, it further comprisesa gas-holder adapted to be in fluid communication with the inlet of saidinjection means;

[0100] it further comprises a pump for injecting water, the pump havingan outlet adapted to be in fluid communication with at least oneinjection well;

[0101] it further comprises means for preparing a gaseous mixture, thepower plant being adapted to be in fluid communication with saidproduction well and/or with the separator through said means forpreparing a gaseous mixture;

[0102] it further comprises a waste-heat boiler adapted to be in fluidcommunication with the exhaust gas outlet;

[0103] the outlet of said injection means is adapted to be in fluidcommunication with at least one production well;

[0104] it further comprises means for separating gases, said means forseparating gases is adapted to be in fluid communication with saidinjection means and with the exhaust gas outlet;

[0105] it further comprises means for purifying the exhaust gases, saidmeans for purifying the exhaust gases is adapted to be in fluidcommunication with said injection means and with the exhaust gas outlet;

[0106] the power plant further comprises a cooling system with a heatexchanger;

[0107] said means for preparing a gaseous mixture is further adapted tobe in fluid communication with said injection means;

[0108] the waste-heat boiler is further adapted to be in fluidcommunication with said injection means;

[0109] the waste-heat boiler is further adapted to be in fluidcommunication with the pump; the heat exchanger is further adapted to bein fluid communication with said injection means and/or the pump.

[0110] Technical result according to the second embodiment of theinvented system, comprising:

[0111] a power plant with an electrical generator, the power planthaving an exhaust gas outlet and being adapted to be in fluidcommunication with at least one production well through a separator,

[0112] an injection means having an outlet adapted to be in fluidcommunication with at least one injection well,

[0113] is achieved due to the fact, that

[0114] the power plant comprises a gas engine, or a gas turbine engineor a gas-diesel engine, any of said engines is adapted to dischargeexhaust gases, which comprise nitrogen and carbon dioxide as theircomponents,

[0115] the electrical generator being connected via mechanical drivemeans with the gas engine, or the gas turbine engine, or the gas-dieselengine,

[0116] and the exhaust gas outlet being in fluid communication with aninlet of said injection means;

[0117] the power plant is in additional fluid communication with saidproduction well;

[0118] the power plant has more than one exhaust gas outlet;

[0119] said injection means comprises a compressor;

[0120] it further comprises a gas-holder adapted to be in fluidcommunication with the inlet of said injection means;

[0121] it further comprises a pump for injecting water, the pump havingan outlet adapted to be in fluid communication with at least oneinjection well;

[0122] it further comprises means for preparing a gaseous mixture, thepower plant being adapted to be in fluid communication with saidproduction well and/or with the separator through said means forpreparing a gaseous mixture;

[0123] it further comprises a waste-heat boiler adapted to be in fluidcommunication with the exhaust gas outlet;

[0124] the outlet of said injection means is adapted to be in fluidcommunication with at least one production well;

[0125] it further comprises means for separating gases, said means forseparating gases is adapted to be in fluid communication with saidinjection means and with the exhaust gas outlet;

[0126] it further comprises means for purifying the exhaust gases, saidmeans for purifying the exhaust gases is adapted to be in fluidcommunication with said injection means and with the exhaust gas outlet;

[0127] the power plant further comprises a cooling system with a heatexchanger;

[0128] said means for preparing a gaseous mixture is further adapted tobe in fluid communication with said injection means;

[0129] the waste-heat boiler and/or the heat exchanger are/is furtheradapted to be in fluid communication with said injection means and/orwith the pump.

[0130] The application of an injection device, for example, a compressorto be used to inject the power plant exhaust gases into ahydrocarbon-bearing formation is well known/see: RU patent No 2046933C1, cl. E21B 43/24, published on 27 Oct. 1995/. However, said technicalresult cannot be achieved, because a steam generator (where steam andflue gases are produced) is not in fluid communication with productionwells or with a separator (accordingly, a gaseous mixture, separatedfrom the produced fluid, is not used to produce a steam-gas mixture).And, also, because the energy is consumed for the production of thesteam, which is to be injected. Injection of exhaust gases of the powerplant results in reduced quality of a gaseous mixture separated from theproduced fluid, owing to increased concentration of the exhaust gases ofthe power plant. To produce hydrocarbons from the separated gaseousmixture it becomes necessary to employ gas separation equipment (whichleads to increased energy consumption). According to the knownsystem/see: USSR Inventors Certificate No 21729300 A3, cl. E21B 43/24,published on 23 Apr. 1992/, the power plant (comprising an electricalgenerator) is adapted to be in fluid communication (through a separator)with said at least one production well. However, said technical resultcannot be achieved, because energy is consumed to produce the portion ofthe steam, which is to be injected. Said technical result in theinvented system is achieved thanks to the fact, that together with otheressential features disclosed in the claims, a power plant with anelectrical generator is used, the power plant comprising a gas engine,or a gas-turbine engine, or a gas-diesel engine, and, the power plant isadapted to be in fluid communication:

[0131] with at least one production well (in the first embodiment of theinvented system);

[0132] with at least one production well through a separator (in thesecond embodiment of the invented system).

[0133] This will allow, when injecting a working substance (the workingsubstance comprises at least a part of the power plant exhaust gasescomprising nitrogen and carbon dioxide as their components), forexample, into an oil-bearing formation through injection wells, toincrease oil recovery from production wells. Also, the production of agaseous mixture separated from the recovered oil-containing fluid(within the limits of a given example we will call the gaseous mixture,separated from the recovered oil-containing fluid, “hydrocarbon gas”)will be increased. Accordingly, this will allow to increase thehydrocarbon gas supply into the power plant with the electricalgenerator:

[0134] from at least one said production well (in the first embodimentof the invented system);

[0135] from the separator (in the second embodiment of the inventedsystem).

[0136] This will provide for a possibility to increase an amount ofenergy generated by the power plant (for example: a) electrical energy;or b) electrical energy and heat energy) and an amount of the producedworking substance. The increase of the production of the hydrocarbon gas(accordingly, the increase of the amount of the energy generated by thepower plant and the increase of the amount of the produced workingsubstance) corresponds not only with the increase in the oil recovery,that is, the increase of the production of the hydrocarbon gas is notonly in proportion with the increase in the oil recovery, but it is alsoconditioned by the increase of the gas factor, since gaseoushydrocarbons are extracted from an oil-containing fluid present in theformation, when the formation oil-containing fluid is affected upon bythe working substance (comprising nitrogen and carbon dioxide). Forexample, an increase of a gas factor was achieved, when formationoil-containing fluid was affected upon by carbon dioxide, and itresulted in 30-35% increase of the produced gaseous hydrocarbons amountand, accordingly, the value of the gas factor increased. Said 30-35%increase of the value of the gas factor has been achieved, due to theability of the carbon dioxide to extract gaseous hydrocarbons fromoil-containing fluid. An amount of gaseous hydrocarbons extracted fromheavy oil (said oil, after its separation from formation oil-containingfluid has been affected upon by carbon dioxide) may be equal to anamount of gaseous hydrocarbons, separated from the formationoil-containing fluid/see: Mirsayapova, L. I. Extraction of lighthydrocarbons from degassed oil under effect of CO₂//Geology, oilrecovery, physics and reservoir hydrodynamics/Works TatNIPIneft. Kazan:Tatarskoye Publishing House, 1973, Vol. No 22, p. 233, p. 236, p. 238;Vakhitov G. G., Namiot A. Yu., Skripka V. G. et al. Study of oildisplacement with nitrogen on reservoir model at pressures up to 70 MPa.//Neftianoye khozyastvo, 1985, X21, p. 37/. During the process ofinjecting the working substance into the formation the concentration ofnitrogen and carbon dioxide in the hydrocarbon gas will also rise due toworking substance breakthrough into the production wells. For example,the carbon dioxide concentration in hydrocarbon gas (Schedel R. L in hisarticle uses the term <<associated gas>>) can increase up to the levelsof 90% after a period of 6 months of carbon dioxide injection/see:Schedel R. L. EOR+CO₂=A gas processing challenge. //Oil and Gas Journal,1982, Vol. 80, N 43, Oct. 25, p. 158/. Accordingly, the hydrocarbon gasquality will decrease because of considerable nitrogen and carbondioxide presence, and the hydrocarbon gas ability to burn willdeteriorate.

[0137] That is, the increase in oil recovery and simultaneous increasein energy (for example: a) electrical energy; or b) electrical energyand heat energy) generated by the power plant and the working substanceproduction is achieved. Wherein, the increase of energy (and the workingsubstance) production grows more intensively than the increase in theoil recovery. Together with this, the hydrocarbon gas quality decreasesbecause of nitrogen and carbon dioxide presence, and the hydrocarbon gasability to burn will deteriorate. Gas-condensate recovery fromgas-condensate reservoirs goes in a similar manner. The gas-condensaterecovery is increased, and an amount of a gaseous mixture separated fromthe recovered fluid is increased. Wherein, the increase in the amount ofthe gaseous mixture is achieved also thanks to the gaseous hydrocarbonsextracted from the retrograde gas-condensate. Wherein, the quality ofthe gaseous mixture separated from the fluid decreases because ofconsiderable presence of inert gas, such as, nitrogen and carbondioxide.

[0138] Effective combustion of the separated gaseous mixture comprisinghydrocarbon constituents and a considerable amount of inert gas (forexample, such as, nitrogen and carbon dioxide) is realized thanks to thepower plant comprising a gas engine, or a gas turbine engine, or agas-diesel engine. Any of these engines is adapted to produce aflammable and pressurized gas-air mixture prior to said combustion. Thisallows to widen the limits of flammability of the gas-air mixture and,accordingly, to ensure the combustion of the separated gaseous mixturecomprising hydrocarbon constituents and a considerable amount ofnitrogen and carbon dioxide. For example, when pressure is increased upto 1 MPa (that is, from 0.1 MPa to 1 MPa), the limits of flammability ofthe methane-air mixture widen to approximately twice as much incomparison with standard conditions, due to upper limit of flammabilitybeing increased./see: Lewis B., Elbe G. Combustion, flames andexplosions of gases.—Moscow: Mir, 1968, p. 575/.

[0139] Thus, the increase in liquid hydrocarbons recovery andsimultaneous increase in the generated energy (and the workingsubstance) is achieved. Wherein, the increase of energy (and the workingsubstance) production grows more intensively than the increase in theliquid hydrocarbons recovery. Accordingly, thanks to the given property,the decrease of specific energy consumption (here, “energy is the energyreceived from exterior producers) to produce hydrocarbons fromhydrocarbon-bearing formations is achieved. For example, from anoil-bearing formation, or, from an oil-bearing formation with a gas cap,or, for example, from a gas-condensate reservoir, or, from a natural gasreservoir, where natural gas is wet gas.

[0140] Schematic diagram shown on FIG. 2 illustrates the embodiments ofthe system of the present invention. The first embodiment of theinvented system comprises: a power plant 1 with an electrical generator2, the power plant 1 having an exhaust gas outlet 3, the power plantcomprising a gas engine 4 (which can be replaced by either a gas turbineengine or a gas-diesel engine) and the electrical generator 2, theshafts of which are connected via mechanical drive means 6 (any meansproviding a mechanical connection of the gas engine's shaft and thegenerator's shaft), the power plant 1 being adapted to be in fluidcommunication with production wells 8; an injection unit 10, theinjection unit 10 having an inlet 11 being in fluid communication withthe exhaust gas outlet 3 and an outlet 12 adapted to be in fluidcommunication with injection wells 14. The injection unit 10 maycomprise a compressor, and the outlet 12 of the injection unit 10 may beadapted to be in fluid communication with the production wells 8. Thepower plant 1 may have more than one exhaust gas outlet and may have acooling system 5 with a heat exchanger 9. Besides, the first embodimentof the invented system may comprise: a separator 7, through which thepower plant 1 may have an additional fluid communication with theproduction wells 8; an electrical heater 13; a waste-heat boiler 15,through which the exhaust gas outlet 3 is in fluid communication withthe injection unit 10; an exhaust gas purification unit 16, throughwhich the exhaust gas outlet 3 is in fluid communication with theinjection unit 10; a gas separation unit 17, through which the exhaustgas outlet 3 is in fluid communication with the injection unit 10; agas-holder 18 adapted to be in fluid communication with the inlet 11 ofthe injection unit 10; a distribution unit 19; an injection unit 20,which may be a compressor, a unit 21 for preparing a gaseous mixture (wewill call the unit 21 “the preparation unit 21”), through which thepower plant 1 is adapted to be in fluid communication with theproduction wells 8 and/or with the separator 7; a water treatment plant22; a pump 23; a pump 24 with an outlet 25 adapted to be in fluidcommunication with the injection wells 14, the pump 24 is adapted to bein fluid communication with the waste-heat boiler 15 and/or the heatexchanger 9; a distribution unit 26; an electrical heater 27; valves28-75. We will make a special note regarding the use of the term “well”:we will consider, that means for the well operation (for example, tubingstring), located within the limits of the well, is a part of the well(also, as in/see: Korotayev Yu. P., Shirkovsky A. I. Recovery,transportation and subterranean storage of gas.—Moscow: Nedra, 1984, p.60; Handbook on oil recovery/Edited by Gimatudinov Sh. K.—Moscow: Nedra,1974, p. 403/). Accordingly, the term swell” will include means for thewell operation (as a part of the well), necessary for its performance ina desired operating mode and for the well to fulfill its functions.

[0141] In the first embodiment of the invented system a separatedgaseous mixture (containing gaseous hydrocarbons) enters the power plant1 from the production wells 8. For example, when an oil-well is equippedwith a sucker-rod pump with a gas anchor (not shown). A gaseous mixture,separated in the production wells 8 (for example, gas, separated fromoil-containing fluid), or a part of it enters the power plant 1 from anannular space (for example, from the space between a tubing string and acasing) of the production wells 8, when the valves 69, 66 are shut, andthe valves 63, 65, 67 are open. Alternatively, at least a part of aseparated gaseous mixture may pass into the power plant 1 from a tubingstring of the production wells 8 (the valves 64, 65, 68 are open). Forexample, when the tubing string is adapted to produce the separatedgaseous mixture by recovering the gaseous mixture from a gas cap of ahydrocarbon-bearing formation. Also, a gaseous mixture may be separatedfrom hydrocarbon-containing fluid in the separator 7, and at least apart of it may be additionally directed into the power plant 1 (thevalves 52, 69 are open). Hydrocarbon-containing fluid, usually comprisesoil, gas and water, if the hydrocarbon-bearing formation is anoil-bearing formation; hydrocarbon-containing fluid, recovered from agas-condensate reservoir, usually comprises gas-condensate, gas andwater. Alternatively, prior to entering the power plant 1, said at leasta part of the separated gaseous mixture may be directed from theseparator 7 and/or the production wells 8 (using the valves 63-69) intothe preparation unit 21, where it is prepared for combustion in thepower plant 1. For example, if said at least a part of the separatedgaseous mixture enters into the preparation unit 21 from the annularspace of the production wells 8, the valves 64, 65, 68, 69 are shut andthe valves 63, 67, 66 are open. Sulfur containing substances, solidparticles, moisture and other contaminants are removed from said atleast a part of the separated gaseous mixture in the preparation unit21; so as to decrease their concentration down to the desired level inaccordance with the requirements demanded from the composition ofmixtures intended for combustion in the power plant 1. Also, in thepreparation unit 21 the working substance contained in said at least apart of the separated gaseous mixture may be separated from said atleast a part of the separated gaseous mixture, when there is anexcessive amount of the working substance in said at least a part of theseparated gaseous mixture. The separated working substance is directedinto the injection unit 10 (the valve 59 is open). A gas-holder (notshown) may be a part of the preparation unit 21 to ensure a continuoussupply of said at least a part of the separated gaseous mixture. Said atleast a part of the separated gaseous mixture is directed from thepreparation unit 21 into the power plant 1.

[0142] Said at least a part of the separated gaseous mixture iscombusted in the gas engine 4 (which can be replaced by either a gasturbine engine or a gas-diesel engine) which drives the electricalgenerator 2. Exhaust gases, resulting from said combustion in the powerplant 1, comprise carbon dioxide and nitrogen. A mixture comprisingcarbon dioxide and nitrogen is an effective working substance to affecta hydrocarbon-bearing formation. Concentration of carbon dioxide andnitrogen in dry exhaust gases of the power plant 1 may be as much as 90%and even more. The working substance (that is, at least a part of theexhaust gases of the power plant 1) is directed through the exhaust gasoutlet 3 to the inlet 11 of the injection unit 10 (the valves 70, 72, 75are shut, the valves 71, 73, 74 are open), and from the injection unit10 (through outlet 12) the working substance is fed under pressure intothe injection wells 14 (the valves 30, 29, 31, 54, 57 are shut, thevalves 28, 32, 33, 58, 53 are open). Distribution of the workingsubstance between the injection wells 14 may be done in the distributionunit 19 and when using the valves 40-47. Alternatively, the exhaustgases, after being produced in the power plant 1, may be directed intothe waste-heat boiler 15 through the exhaust gas outlet 3 (prior togetting to the inlet 11 of the injection unit 10), when the valve 74 isshut, the valve 75 is open. A temperature of the exhaust gases of thepower plant 1 may be about 350-400° C.

[0143] The exhaust gases are cooled while transferring their heat energyto other heat-carriers in the waste-heat boiler 15. For example, water,which is to be injected into the hydrocarbon-bearing formation, and theworking substance (after its passage through the injection unit 10) maybe such heat-carriers. Also, the working substance may be directed intothe exhaust gas purification unit 16 through the exhaust gas outlet 3or, for example, from the waste-heat boiler 15 (prior to getting to theinlet 11 of the injection unit 10), when the valve 71 is shut, the valve70 is open. The working substance is treated for removal of corrosivesubstances (oxygen, nitrogen oxides and some others), solid particlesand moisture down to the desired level in the exhaust gas purificationunit 16. Additionally, the working substance may be directed into thegas separator unit 17 through the exhaust gas outlet 3 or, for example,from the exhaust gas purification unit 16 (prior to getting to the inlet11 of the injection unit 10), when the valve 73 is shut, the valve 72 isopen. The working substance treatment to the desirable composition isperformed by reducing the concentration of nitrogen in the workingsubstance in the gas separation unit 17. Also, the treatment of theworking substance to the desirable composition may be performed byintroducing certain constituents into it. Besides, the working substancemay be directed into the gas-holder 18 through the exhaust gas outlet 3or, for example, from the gas separation unit 17 (prior to getting tothe inlet 11 of the injection unit 10), when the valve 62 is open. Whichmay be realized with excessive amount of the working substance being fedto the inlet 11 of the injection unit 10. A part of the workingsubstance may be fed from the gas-holder 18 to the inlet 11 of theinjection unit 10, if the insufficient amount of the working substanceis fed to the inlet 11 of the injection unit 10. Also, the workingsubstance (after its passage through the injection unit 10, which maycomprise a compressor) may be heated in the heat exchanger 9 and/or thewaste-heat boiler 15. For example, the working substance may be directedinto the waste-heat boiler 15 (prior to the working substance beinginjected into the injection wells 14), when the valves 28, 31, 32, 30are shut, the valves 29, 33 open. Additionally, the working substancemay be heated in an electrical heater 13. The working substance may bedirected into the electrical heater 13 (prior to the working substancebeing injected into the injection wells 14), when the valves 57, 53 areshut, the valves 58, 54 open. Besides, the working substance may bedirected into the injection unit 20 (the valve 58 is shut, the valve 57is open) to increase the working substance pressure prior to the workingsubstance being injected into the injection wells 14. In addition to theabove, the working substance may be injected into the formation throughthe production wells 8, using the injection unit 10, to treat a zone ofthe formation in the vicinity of the production wells 8 (when the valves63, 64, 67, 68, 52, 30, 29, 31, 54, 57 are shut, and the valves 28, 32,33, 58, 53 are open). The working substance may be injected through thewells using a tubing string or an annular space of the wells anddistributed by the valves 44-51.

[0144] Also, water may be injected into the formation through theinjection wells 14. For this, the water from water treatment plant 22 ispassed into pumps 24. The water is fed by the pumps 24 into theinjection wells 14 (the valves 36, 35, 37, 61, 56 are shut, the valves60, 55, 34, 39, 38 are open). The water may be distributed between theinjection wells 14 through a distribution unit 26. If it is necessary,the temperature of the water may be increased. For this, the water isdirected into the heat exchanger 9 and/or into the waste-heat boiler 15using the valves 34-39. And, the water is heated according to thegeological-and-physical characteristic and the development stage of theformation. For example, the water to be heated is directed only into thewaste-heat boiler 15, if the valves 34, 38, 37, 36 are shut and thevalves 39, 35 are open. Additionally, the water may be heated in theelectrical heater 27. The water is directed into the electrical heater27 with the help of the valves 56, 55, 60, 61. The water may be directedinto the pump 23 (the valve 60 is shut, the valve 61 is open) toincrease the water pressure prior to the water being injected into theinjection wells 14. The water may be injected into one injection well orinto a plurality of wells simultaneously with the working substance (forexample, when mixing the water with the working substance in aninjection well), or one after another. Alternatively, a group ofinjection wells is used to inject the working substance, and anothergroup of injection wells is used to inject water. The working substanceand the water (which are distributed through the valves 40-47) may beinjected through the injection wells using the tubing string or theannular space of the injection wells.

[0145] Example: electrical energy consumed to realize oil recovery andother technological processes performed at an oil-field (withoutconsidering the electrical energy consumed to realize gas injection) isequal to approximately 163-192 kWh per one ton of produced oil/see:Aroutyunov A. I., Louzin V. I., Maximov V. P. et al. New trends in useof hydrocarbon gas //Ekonomika i organizatsiia promishlennogoproizvodstva, 1980, No 10 (76), p. 67, p.68, p. 70/. A gas factor isequal to 120 m³/t; 50% of the gaseous mixture is separated from anoil-containing fluid in production wells. The gaseous mixture, separatedfrom the fluid, is combusted in a power plant (or power plants). Thepower plant comprises a gas engine having the compression ratio value of10. The gas engine drives an electrical generator. The working substance(exhaust gases of the power plant or the power plants) is injected intothe formation through injection wells. The electrical energy consumed torealize the injection of the working substance is equal to 80 kWh perone ton of produced oil. In the beginning of the working substanceinjection, gaseous hydrocarbons constitute approximately 100% of theseparated from the produced fluid gaseous mixture. The lower heatingvalue of the gaseous hydrocarbons equals (75% of mass of gaseoushydrocarbons molecules is carbon) to Q_(H)≈36×10⁶ Joule/m³; the upperlimit and the lower limit of flammability of the gas-air mixture (whenpressure is equal to 1 MPa, and temperature is equal to 20° C.) will berespectively about 23.5% and about 4.49%/see: Lewis B., Elbe G.Combustion, flames and explosions of gases.—Moscow: Mir, 1968, p. 575/.When supplying 300 m³/h of the gaseous mixture (which is ensured by oilproduction of 120 t/day) into the power plant in the beginning of theworking substance injection into the formation, useful power, given bythe generator of the power plant to users, will be P≈900 kW, heatenergy, given to heat carriers (for example, water) will be Q≈1.29×10⁹cal/h Wherein, nitrogen and carbon dioxide (contained as components ofthe exhaust gases of the power plant) are discharged from the powerplant in the amount of V_(p)≈2556 m³/h (including, carbon dioxide morethan 11%). Thus, with the given conditions—in the beginning of theworking substance injection, when 1 ton of oil is produced,approximately 180 kWh of electrical energy may be generated by the powerplant (where the separated from the fluid gaseous mixture is utilized asgaseous fuel). Accordingly, the specific energy consumption (here,“energy” is the energy received from exterior producers) to realize theoil recovery and other technological processes performed at an oil-fieldwill be not more than 92 kWh per 1 ton of recovered oil.

[0146] With the daily oil production increased by 10%, the supply of thegaseous mixture into the power plant will also increase (which isinterrelated with the increase in oil production, and is caused by theincrease of the gas factor, said gas factor increase is realized alsodue to the ability of the working substance to extract gaseoushydrocarbons from oil-containing fluid present in the formation), and itwill be about 800 m³/h (this will also include about 400 m³/h of gaseoushydrocarbons). Accordingly, the gaseous mixture comprises 50% of inertgas (which consists of 90% of nitrogen and 10% of carbon dioxide) and50% of gaseous hydrocarbons (the lower heating value of the gaseoushydrocarbons is Q_(H≅)36×10⁶ Joule/m³, wherein 75% of mass of gaseoushydrocarbons molecules is carbon). When supplying said volume of thegaseous mixture with said composition into the power plant, the usefulpower, given by the generator of the power plant to users, will beP≈1200 kW, heat energy, given to heat carriers (for example, water) willbe Q_(H)≈1.72×10⁹ cal/h. Wherein, nitrogen and carbon dioxide (containedas components of the exhaust gases of the power plant) are dischargedfrom the power plant in the amount of V_(p)≈3808 m³/h (including, carbondioxide more than 11%). The upper limit and the lower limit offlammability of the gas-air mixture (when pressure is equal 1 MPa, andtemperature is equal to 20° C.) will be respectively about 37.4% andabout 8.61% (as far as, the combustible constituent is concerned, therespective values will be about 18.7% and about 4.05%). Thus, with thegiven conditions, when 1 ton of oil is produced, approximately 218 kWhof electrical energy may be generated by the power plant (where theseparated from the fluid gaseous mixture is utilized as gaseous fuel).Accordingly, the specific energy consumption (here. “energy” is theenergy received from exterior producers) to realize the oil recovery andother technological processes performed at an oil-field will be not morethan 54 kWh per 1 ton of recovered oil.

[0147] The second embodiment of the invented system comprises: a powerplant 1 with an electrical generator 2, the power plant 1 having anexhaust gas outlet 3, the power plant comprising a gas engine 4 (whichcan be replaced by either a gas turbine engine or a gas-diesel engine)and the electrical generator 2, the shafts of which are connected viamechanical drive means 6 (any means providing a mechanical connection ofthe engine's shaft and the generator's shaft); a separator 7, the powerplant 1 being adapted to be in fluid communication with production wells8 through the separator 7; an injection unit 10, the injection unit 10having an inlet 11 being in fluid communication with the exhaust gasoutlet 3 and an outlet 12 adapted to be in fluid communication withinjection wells 14. The injection unit 10 may comprise a compressor, andthe outlet 12 of the injection unit 10 may be adapted to be in fluidcommunication with the production wells 8. The power plant 1 may havemore than one exhaust gas outlet and a cooling system 5 with a heatexchanger 9, and may have an additional fluid communication with theproduction wells 8. Besides, the second embodiment of the inventedsystem may comprise: a waste-heat boiler 15, through which the exhaustgas outlet 3 is in fluid communication with the injection unit 10; anelectrical heater 13; an exhaust gas purification unit 16, through whichthe exhaust gas outlet 3 is in fluid communication with the injectionunit 10; a gas separation unit 17, through which the exhaust gas outlet3 is in fluid communication with the injection unit 10; a gas-holder 18adapted to be in fluid communication with the inlet 11 of the injectionunit 10; a distribution unit 19; an injection unit 20, which may be acompressor; a unit 21 for preparing a gaseous mixture (we will call theunit 21 “the preparation unit 21”), through which the power plant 1 isadapted to be in fluid communication with the production wells 8 and/orwith the separator 7; a water treatment plant 22; a pump 23; a pump 24with an outlet 25 adapted to be in fluid communication with theinjection wells 14, the pump 24 is adapted to be in fluid communicationwith the waste-heat boiler 15 and/or the heat exchanger 9; adistribution unit 26; an electrical heater 27; valves 28-75.

[0148] In the second embodiment of the invented system a separatedgaseous mixture (containing gaseous hydrocarbons) enters the power plant1 from the separator 7. For example, when flowing oil well operation isemployed, or, for example, when sucker-rod pumps (not shown) forrecovering oil from oil wells are employed. Hydrocarbon-containing fluidis recovered from a hydrocarbon-bearing formation and is directed fromthe production wells 8 into the separator 7 (the valve 52 is open). Thehydrocarbon-containing fluid, usually comprises oil, gas and water, ifthe hydrocarbon-bearing formation is an oil-bearing formation;hydrocarbon-containing fluid, recovered from a gas-condensate reservoir,usually comprises gas-condensate, gas and water. A gaseous mixture isseparated from the hydrocarbon-containing fluid in the separator 7. Andat least a part of the separated gaseous mixture is directed from theseparator 7 into the power plant 1 (the valve 66 is shut, the valves 52,69, 65 are open).

[0149] Besides said at least a part of the separated gaseous mixtureentering the power plant 1 from the separator 7, at least a part of agaseous mixture, separated from hydrocarbon-containing fluid in theproduction wells 8, may be additionally directed into the power plant 1from the production wells 8. For example, when it is necessary todecrease pressure in the annular space (the valves 63, 67 are open) or,for example, when recovering a gaseous mixture from a gas cap, when thehydrocarbon-bearing formation is an oil-bearing formation with a gascap. Alternatively, prior to entering the power plant 1, said at least apart of the separated gaseous mixture may be directed from the separator7 and/or the production wells 8 (using the valves 63-69) into thepreparation unit 21, where it is prepared for combustion in the powerplant 1. For example, if said at least a part of the separated gaseousmixture enters into the preparation unit 21 from the separator 7, thevalves 63, 64, 65, 67, 68, are shut and the valves 69, 66 are open.Sulfur containing substances, solid particles, moisture and othercontaminants are removed from said at least a part of the separatedgaseous mixture in the preparation unit 21 so, that to decrease theirconcentration down to the desired level in accordance with therequirements demanded from the composition of mixtures intended forcombustion in the power plant 1. Also, in the preparation unit 21 theworking substance contained in said at least a part of the separatedgaseous mixture may be separated from said at least a part of theseparated gaseous mixture, when there is an excessive amount of theworking substance in said at least a part of the separated gaseousmixture. The separated working substance is directed into the injectionunit 10 (the valve 59 is open). A gas-holder (not shown) may be a partof the preparation unit 21 to ensure a continuous supply of said atleast a part of the separated gaseous mixture. Said at least a part ofthe separated gaseous mixture is directed from the preparation unit 21into the power plant 1.

[0150] Said at least a part of the separated gaseous mixture iscombusted in the gas engine 4 (which can be replaced by either a gasturbine engine or a gas-diesel engine) which drives the electricalgenerator 2. Exhaust gases, resulting from combustion in the power plant1, comprise carbon dioxide and nitrogen. A mixture comprising carbondioxide and nitrogen is an effective working substance to affect ahydrocarbon-bearing formation. Concentration of carbon dioxide andnitrogen in dry exhaust gases of the power plant 1 may be as much as 90%and even more. The working substance (that is, at least a part of theexhaust gases of the power plant 1) is directed through the exhaust gasoutlet 3 to the inlet 11 of the injection unit 10 (the valves 70, 72, 75are shut, the valves 71, 73, 74 are open), and from the injection unit10 (through outlet 12) the working substance is fed under pressure intothe injection wells 14 (the valves 30, 29, 31, 54, 57 are shut, thevalves 28, 32, 33, 58, 53 are open). Distribution of the workingsubstance between the injection wells 14 may be done in the distributionunit 19 and when using the valves 40-47. Alternatively, the exhaustgases, after being produced in the power plant 1, may be directed intothe waste-heat boiler 15 through the exhaust gas outlet 3 (prior togetting to the inlet 11 of the injection unit 10), when the valve 74 isshut, the valve 75 is open. A temperature of the exhaust gases of thepower plant 1 may be about 350-400° C. The exhaust gases are cooledwhile transferring their heat energy to other heat-carriers in thewaste-heat boiler 15. For example, water, which is to be injected intothe hydrocarbon-bearing formation, and the working substance (after itspassage through the injection unit 10) may be such heat-carriers. Also,the working substance may be directed into the exhaust gas purificationunit 16 through the exhaust gas outlet 3 or, for example, from thewaste-heat boiler 15 (prior to getting to the inlet 11 of the injectionunit 10), when the valve 71 is shut, the valve 70 is open. The workingsubstance is treated for removal of corrosive substances (oxygen,nitrogen oxides and some others), solid particles and moisture down tothe desired level in the exhaust gas purification unit 16. Additionally,the working substance may be directed into the gas separation unit 17through the exhaust gas outlet 3 or, for example, from the exhaust gaspurification unit 16 (prior to getting to the inlet 11 of the injectionunit 10), when the valve 73 is shut, the valve 72 is open. The workingsubstance treatment to the desirable composition is performed byreducing the concentration of nitrogen in the working substance in thegas separation unit 17. Also, the treatment of the working substance tothe desirable composition may be performed by introducing certainconstituents into it. Besides, the working substance may be directedinto the gas-holder 18 through the exhaust gas outlet 3 or, for example,from the gas separation unit 17 (prior to getting to the inlet 11 of theinjection unit 10), when the valve 62 is open. Which may be realizedwith excessive amount of the working substance being fed to the inlet 11of the injection unit 10. A part of the working substance may be fedfrom the gas-holder 18 to the inlet 11 of the injection unit 10, if theinsufficient amount of the working substance is fed to the inlet 11 ofthe injection unit 10. Also, the working substance (after its passagethrough the injection unit 10) may be heated in the heat exchanger 9and/or the waste-heat boiler 15. For example, the working substance maybe directed into the waste-heat boiler 15 (prior to the workingsubstance being injected into the injection wells 14), when the valves28, 31, 32, 30 are shut, the valves 29, 33 open. Additions, the workingsubstance may be heated in an electrical heater 13. The workingsubstance may be directed into the electrical heater 13 (prior to theworking substance being injected into the injection wells 14), when thevalves 57, 53 are shut, the valves 58, 54 open. Besides, the workingsubstance may be directed into the injection unit 20 (the valve 58 isshut, the valve 57 is open) to increase the working substance pressureprior to the working substance being injected into the injection wells14. In addition to the above, the working substance may be injected intothe formation through the production wells 8, using the injection unit10, to treat a zone of the formation in the vicinity of the productionwells 8 (in this case the valves 63, 64, 67, 68, 52, 30, 29, 31, 54, 57are shut, and the valves 28, 32, 33, 58, 53 are open). The workingsubstance may be injected through the wells using a tubing string or anannular space of the wells and distributed by the valves 44-51.

[0151] Also, water may be injected into the formation through theinjection wells 14. For this, the water from water treatment plant 22 ispassed into pumps 24. The water is fed by the pumps 24 into theinjection wells 14 (the valves 36, 35, 37, 61, 56 are shut, the valves60, 55, 34, 39, are 38 open). The water may be distributed between theinjection wells 14 through a distribution unit 26. If it is necessary,the temperature of the water may be increased. For this, the water isdirected into the heat exchanger 9 and/or into the waste-heat boiler 15using the valves 34-39. And, the water is heated according to thegeological-and-physical characteristic and the development stage of theformation. For example, the water to be heated is directed only into thewaste-heat boiler 15, if the valves 34, 38, 37, 36 are shut and thevalves 39, 35 are open. Additionally, the water may be heated in theelectrical heater 27. The water is directed into the electrical heater27 with the help of the valves 56, 55, 60, 61. The water may be directedinto the pump 23 (the valve 60 is shut, the valve 61 is open) toincrease the water pressure prior to the water being injected into theinjection wells 14. The water may be injected into one injection well orinto a plurality of wells simultaneously with the working substance (forexample, when mixing the water with the working substance in aninjection well), or one after another. Alternatively, a group ofinjection wells is used to inject the working substance, and anothergroup of injection wells is used to inject water. The working substanceand the water (which are distributed through the valves 40-47) may beinjected through the injection wells using the tubing string or theannular space of the injection wells.

[0152] Example: electrical energy consumed to realize oil recovery andother technological processes performed at an oil-field (withoutconsidering the electrical energy consumed to realize gas injection) isequal to approximately 163-192 kWh per one ton of produced oil /see:Aroutyunov A. I., Louzin V. I., Maximov V. P. et al. New trends in useof hydrocarbon gash Ekonomika i organizatsiia promishlennogoproizvodstva, 1980, No 10 (76), p. 67, p. 68, p. 70/. A gas factor isequal to 100 m³/t; 60% of the gaseous mixture is separated fromoil-containing fluid during the first stage of separation. The gaseousmixture, separated from the fluid, is combusted in a power plant (orpower plants). The power plant comprises a gas engine having thecompression ratio value of 10. The gas engine drives an electricalgenerator. The working substance (exhaust gases of the power plant orthe power plants) is injected into the formation through injectionwells. The electrical energy consumed to realize the injection of theworking substance is equal to 80 kWh per one ton of produced oil. In thebeginning of the working substance injection, gaseous hydrocarbonsconstitute approximately 100% of the separated from the produced fluidgaseous mixture. The lower heating value of the gaseous hydrocarbons(75% of mass of gaseous hydrocarbons molecules is carbon) equals toQ_(H)≈36×10⁶ Joule/m³; the upper limit and the lower limit offlammability of the gas-air mixture (when pressure is equal to 1 MPa,and temperature is equal to 20° C.) will be respectively about 23.5% andabout 4.49%/see: Lewis B., Elbe G. Combustion, flames and explosions ofgases.—Moscow: Mir, 1968, p. 575/. When supplying 300 m³/h of thegaseous mixture (which is ensured by oil production of 120 t/day) intothe power plant in the beginning of the working substance injection intothe formation, useful power, given by the generator of the power plantto users, will be P=900 kW, heat energy, given to heat carriers (forexample, water) will be Q≈1.29×10⁹ cal/h. Wherein, nitrogen and carbondioxide (contained as components of the exhaust gases of the powerplant) are discharged from the power plant in the amount of V_(p)≈2556m³/h (including, carbon dioxide more than 11%). Thus, with the givenconditions—in the beginning of the working substance injection, when 1ton of oil is produced, approximately 180 kWh of electrical energy maybe generated by the power plant (where the separated from the fluidgaseous mixture is utilized as gaseous fuel). Accordingly, the specificenergy consumption (here, “energy” is the energy received from exteriorproducers) to realize the oil recovery and other technological processesperformed at an oil-field will be not more than 92 kWh per 1 ton ofrecovered oil.

[0153] With the daily oil production increased by 100/%, the supply ofthe gaseous mixture into the power plant will also increase (which isinterrelated with the increase in oil production and is caused by theincrease of the gas factor, which is realized also due to the ability ofthe working substance to extract gaseous hydrocarbons fromoil-containing fluid present in the formation), and it will be about 800m³/h (this will also include about 400 m³/h of gaseous hydrocarbons).Accordingly, the gaseous mixture comprises 50% of inert gas (whichconsists of 90% of nitrogen and 10% of carbon dioxide) and 50% ofgaseous hydrocarbons (the lower heating value of the gaseoushydrocarbons is Q_(H)≈36×10⁶ Joule/m³, wherein 75% of mass of gaseoushydrocarbons molecules is carbon). When supplying said volume of thegaseous mixture with said composition into the power plant, the usefulpower, given by the generator of the power plant to users, will beP≈1200 kW, heat energy, given to heat carriers (for example, water) willbe Q≈1.72×10⁹ cal/h. Wherein, nitrogen and carbon dioxide (contained ascomponents of the exhaust gases of the power plant) are discharged fromthe power plant in the amount of V_(p)≈3808 m³/h (including, carbondioxide more than 11%). The upper limit and the lower limit offlammability of the gas-air mixture (when pressure is equal to 1 MPa,and temperature is equal to 20° C.) will be respectively about 37.4% andabout 8.61% (as far as, the combustible constituent is concerned, therespective values will be about 18.7% and about 4.05%). Thus, with thegiven conditions, when 1 ton of oil is produced, approximately 218 kWhof electrical energy may be generated by the power plant (where theseparated from the fluid gaseous mixture is utilized as gaseous fuel).Accordingly, the specific energy consumption (here, “energy” is theenergy received from exterior producers) to realize the oil recovery andother technological processes performed at an oil-field will be not morethan 54 kWh per 1 ton of recovered oil.

[0154] When the invented system is operating and when the workingsubstance is injected into a hydrocarbon-bearing formation, a volume ofliquid hydrocarbons, recovered from the formation, increases. Also, avolume of a gaseous mixture separated from a hydrocarbon-containingfluid will increase. Accordingly, this will allow to increase theseparated gaseous mixture supply into the power plant:

[0155] from at least one said production well (in the first embodimentof the invented system);

[0156] from the separator (in the second embodiment of the inventedsystem).

[0157] This will provide for a possibility to increase an amount ofenergy generated by the power plant (for example: a) electrical energy;or b) electrical energy and heat energy) and an amount of the producedworking substance. The increase of the production of the separatedgaseous mixture (accordingly, the increase of the amount of the energygenerated by the power plant and the increase of the amount of theproduced working substance) corresponds not only with the increase inthe liquid hydrocarbon recovery, that is, the increase of the productionof the separated gaseous mixture is not only in proportion with theincrease in the liquid hydrocarbon recovery, but it is also conditionedby the increase of the gas factor, since gaseous hydrocarbons areextracted from an oil-containing fluid present in the formation, whenthe formation oil-containing fluid is affected upon by the workingsubstance. In connection with this, the increase in the liquidhydrocarbons recovery and simultaneous increase in the energy (and theworking substance) generated by the power plant is achieved. Wherein,the increase of energy (and the working substance) production grows moreintensively than the increase in the oil recovery. Together with this,during the process of injecting the working substance into the formationthe concentration of nitrogen and carbon dioxide in the separatedgaseous mixture will also rise due to working substance breakthroughinto the production wells. And the separated gaseous mixture qualitydecreases because of nitrogen and carbon dioxide presence, and theseparated gaseous mixture ability to burn will deteriorate. For example,at the Budafa oilfield block, when injecting gas, comprising about 80%of carbon dioxide, and water, one after another, after 15 months ofinjecting, the separated from oil-containing fluid gas comprised about60% of carbon dioxide/see: Balint V., Ban A., Doleshal Sh. et al: Use ofcarbon dioxide in oil recovery.—Moscow: Nedra, 1977, p.223, p. 224/. Asit has been stated earlier, the carbon dioxide concentration inhydrocarbon gas (Schedel R. L in his article uses the term <<associatedgas>>) can increase up to the levels of 90% after a period of 6 monthsof carbon dioxide injection. Because of this, for example, wheninjecting carbon dioxide into an oil-bearing formation, it will becomenecessary to process 5-10 times the regular amount of hydrocarbon gas(regular amount of the hydrocarbon gas is the amount of the hydrocarbongas before the beginning of the injection process), which comprises upto 80-90% of carbon dioxide/see: Schedel R. L. EOR+CO₂=A gas processingchallenge. //Oil and Gas Journal, 1982, Vol. 80, No 43, Oct. 25, p.158/. Having in mind, that nitrogen has a lower level of solubility thancarbon dioxide in a hydrocarbon-containing fluid, the above statementwill be true when injecting a nitrogen and carbon dioxide mixture intothe formation.

[0158] Thus, nitrogen and carbon dioxide injection into ahydrocarbon-bearing formation is inseparably connected with aconsiderable increase of a gas factor (including, the increase of theamount of the produced gaseous hydrocarbons due to the gaseoushydrocarbons extraction from hydrocarbon-containing fluid present in theformation), which goes along with a considerable increase of nitrogenand carbon dioxide concentration in a gaseous mixture separated from theproduced fluid. Accordingly, the separated gaseous mixture qualitydecreases together with its ability to burn. Effective combustion of theseparated gaseous mixture comprising hydrocarbon constituents and aconsiderable amount of inert gas (for example, such as, nitrogen andcarbon dioxide) is realized in a gas engine, or in a gas turbine engine,or in a gas-diesel engine. Any of these engines is adapted to produce aflammable and pressurized gas-air mixture prior to said combustion. Thisallows to widen the limits of flammability of the gas-air mixture and,accordingly, to ensure the combustion of the separated gaseous mixturecomprising the hydrocarbon constituents and a considerable amount ofnitrogen and carbon dioxide. Accordingly, heat energy released duringthe separated gaseous mixture combustion, and, energy consumed for thegas-air mixture compression (or, for compression of the separatedgaseous mixture and air, which is to be used as oxidant), is transformed(to be exact, the known part of the energy is transformed) intomechanical energy (the latter is transformed into electric energy withthe help of a generator). For example, when a mixture, consisting of 50%of methane and 50% of inert gas (said inert gas contains 90% of nitrogenand 10% of carbon dioxide), is combusted with atmospheric air, the upperlimit and the lower limit of flammability of the gas-air mixture (when,pressure is equal to 1 MPa, and temperature is equal to 20° C.),comprising said mixture and the air, will be respectively 37.4% and8.61% (as far as, the combustible constituent is concerned, therespective values will be 18.7% and 4.05%). That is, combustion of saidmixture may be realized in a gas engine with the compression ratio valueof 10. The same result may be achieved, when a mixture, consisting of10% of methane and 90% of inert gas (said inert gas contains 90% ofnitrogen and 10% of carbon dioxide), is combusted with atmospheric air,the upper limit and the lower limit of flammability of the gas-airmixture (when, pressure is equal to 1 MPa, and temperature is equal to20° C.), comprising said mixture and the air, will be respectively 74.9%and 32.03% (as far as, the combustible constituent is concerned, therespective values will be 7.49% and 3.203%). The calculations were doneusing the data from following works: /see: Lewis B., Elbe G. Combustion,flames and explosions of gases.—Moscow: Mir, 1968, p. 575; Isserlin A.S. The basics of gaseous fuel combustion. Moscow: Nedra, 1987, p.p.69-71/.

[0159] The energy generated by the power plant is used to supplyoilfield equipment, it may be used for heating of injected water and theworking substance, and electrical energy generated by the power plantmay be generated into an electrical network. Thus, the increase inliquid hydrocarbons recovery and simultaneous increase in the producedenergy (and the working substance) is achieved. Wherein, the increase ofenergy (and the working substance) production grows more intensivelythan the increase in the liquid hydrocarbons recovery. Accordingly,thanks to the given property, the decrease of specific energyconsumption (here, “energy” is the energy received from exteriorproducers) to produce hydrocarbons from the hydrocarbon-bearingformation is achieved. For example, from an oil-bearing formation, or,

[0160] Also, the present invention will provide an environmentally saferhydrocarbons production process from a hydrocarbon-bearing formation dueto carbon dioxide being injected into the formation instead of beingreleased into the atmosphere.

What is claimed is:
 1. A method for recovery of hydrocarbons from ahydrocarbon-bearing formation, the method comprising: recovering ahydrocarbon-containing fluid through at least one production well;separating at least a part of a gaseous mixture from the fluid;injecting a gas through at least one injection well; characterized inthat at least a part of the separated gaseous mixture is combusted withair, which is used as oxidant, in a power plant, said air and said atleast a part of the separated gaseous mixture are mixed and a gas-airmixture resulting from said mixing is compressed prior to saidcombustion, or the gas-air mixture is ignited during said compression,exhaust gases resulting from said combustion, which comprise nitrogenand carbon dioxide as their components, are discharged from the powerplant; and at least a part of the exhaust gases is compressed and thenis used as at least a part of said injection gas.
 2. The methodaccording to claim 1, characterized in that electrical energy and/orheat energy are/is produced in the power plant when said combustion ofsaid at least a part of the separated gaseous mixture is realized. 3.The method according to claim 1, characterized in that water is injectedthrough at least one injection well, said injection gas and the waterbeing injected simultaneously or one after another.
 4. The methodaccording to claim 1, characterized in that said air and said at least apart of the separated gaseous mixture are mixed in the power plantand/or the gas-air mixture is compressed in the power plant.
 5. Themethod according to claim 1, characterized in that the gas-air mixtureis compressed during said mixing and/or after said mixing.
 6. The methodaccording to claim 1, characterized in that a pressure of the gas-airmixture is established according to the composition of said at least apart of the separated gaseous mixture when the gas-air mixture is beingcompressed.
 7. The method according to claim 1, characterized in thatsaid at least a part of the separated gaseous mixture and/or said airare/is compressed prior to said mixing.
 8. The method according to claim1, characterized in that the gas-air mixture is heated prior to saidcompression and/or said at least a part of the separated gaseous mixtureis heated prior to said mixing.
 9. The method according to claim 1,characterized in that a ratio between said air contained in the gas-airmixture and combustible constituents of the gas-air mixture ismaintained so, that the gas-air mixture comprises said air in the amountwhich is theoretically necessary for oxidizing the combustibleconstituents of the gas-air mixture, or the gas-air mixture comprisesmore of said air, than it is theoretically necessary for oxidizing thecombustible constituents of the gas-air mixture.
 10. The methodaccording to claim 1, characterized in that a ratio between said aircontained in the gas-air mixture and combustible constituents of thegas-air mixture is maintained so, that the gas-air mixture comprisesless of said air, than it is theoretically necessary for oxidizing thecombustible constituents of the gas-air mixture.
 11. The methodaccording to claim 1, characterized in that the gas-air mixturecomprises said at least a part of the separated gaseous mixture, saidair and a part of the exhaust gases.
 12. The method according to claim1, characterized in that said at least a part of the separated gaseousmixture and/or said air are/is mixed with a part of the exhaust gasesprior to production of the gas-air mixture.
 13. The method according toclaim 1, characterized in that the gas-air mixture is mixed with a partof the exhaust gases prior to said compression of the gas-air mixture orduring said compression of the gas-air mixture.
 14. The method accordingto claim 1, characterized in that said at least a part of the exhaustgases is previously compressed, after which moisture is removed, andthen said at least a part of the exhaust gases is additionallycompressed and is subsequently used as said at least a part of saidinjection gas.
 15. The method according to claims 1, or 2, or 3,characterized in that the water is heated by the heat and/or theelectrical energy prior to the water being injected.
 16. The methodaccording to claims 1, or 2, characterized in that said injection gas isheated by the heat and/or the electrical energy prior to said injectiongas being injected.
 17. The method according to claims 1, or 3, or 15,or 16, characterized in that a pressure and/or a temperature of saidinjection gas and/or of the water are/is established according to ageological-and-physical characteristic and a development stage of theformation.
 18. The method according to claim 1, characterized in that acomposition and a quantity of said injection gas are establishedaccording to a geological-and-physical characteristic and a developmentstage of the formation; specifically, said injection gas is treated to adesirable composition by reducing concentration of nitrogen in said atleast a part of the exhaust gases.
 19. The method according to claim 1,characterized in that said at least a part of the separated gaseousmixture is treated for removal of moisture and/or corrosive substancesprior to said mixing.
 20. The method according to claim 1, characterizedin that liquid or gaseous substances, including combustible substances,are added into the gas-air mixture prior to said combustion.
 21. Themethod according to claim 1, characterized in that said injection gas istreated for removal of moisture and/or corrosive substances prior tosaid injection.
 22. The method according to claim 1, characterized inthat said injection gas is injected through at least one productionwell.
 23. The method according to claim 1, characterized in that said atleast a part of the separated gaseous mixture is separated to producenitrogen and/or carbon dioxide, and then the nitrogen and/or the carbondioxide are/is mixed with said at least a part of the exhaust gases,whereupon, the resulting mixture is used as said at least a part of saidinjection gas.
 24. A method for recovery of hydrocarbons from ahydrocarbon-bearing formation, the method comprising: recovering ahydrocarbon-containing fluid through at least one production well;separating at least a part of a gaseous mixture from the fluid;injecting a gas through at least one injection well; characterized inthat at least a part of the separated gaseous mixture is combusted withair, which is used as oxidant in a power plant, said air and said atleast a part of the separated gaseous mixture are compressed and thenare mixed to produce a gas-air mixture prior to said combustion, or thegas-air mixture is ignited, as soon as it is mixed, exhaust gasesresulting from said combustion, which comprise nitrogen and carbondioxide as their components, are discharged from the power plant; and atleast a part of the exhaust gases is compressed and then is used as atleast a part of said injection gas.
 25. The method according to claim24, characterized in that electrical energy and/or heat energy are/isproduced in the power plant when said combustion of said at least a partof the separated gaseous mixture is realized.
 26. The method accordingto claim 24, characterized in that water is injected through at leastone injection well, said injection gas and the water being injectedsimultaneously or one after another.
 27. The method according to claim24, characterized in that said air and said at least a part of theseparated gaseous mixture are mixed and/or compressed in the powerplant.
 28. The method according to claim 24, characterized in that apressure of said air and a pressure of said at least a part of theseparated gaseous mixture are established according to the compositionof said at least a part of the separated gaseous mixture, when saidcompression of said air and of said at least a part of the separatedgaseous mixture is being realized.
 29. The method according to claim 24,characterized in that said at least a part of the separated gaseousmixture is heated prior to said compression.
 30. The method according toclaim 24, characterized in that a ratio between said air contained inthe gas-air mixture and combustible constituents of the gas-air mixtureis maintained so, that the gas-air mixture comprises said air in theamount, which is theoretically necessary for oxidizing the combustibleconstituents of the gas-air mixture, or the gas-air mixture comprisesmore of said air, than it is theoretically necessary for oxidizing thecombustible constituents of the gas-air mixture.
 31. The methodaccording to claim 24, characterized in that a ratio between said aircontained in the gas-air mixture and combustible constituents of thegas-air mixture is maintained so, that the gas-air mixture comprisesless of said air, than it is theoretically necessary for oxidizing thecombustible constituents of the gas-air mixture.
 32. The methodaccording to claim 24, characterized in that the gas-air mixturecomprises said at least a part of the separated gaseous mixture, saidair and a part of the exhaust gases.
 33. The method according to claim24, characterized in that said at least a part of the separated gaseousmixture and/or said air are/is mixed with a part of the exhaust gasesprior to said combustion or during ignition of the gas-air mixture. 34.The method according to claim 24, characterized in that the gas-airmixture is mixed with a part of the exhaust gases prior to saidcombustion or during ignition of the gas-air mixture.
 35. The methodaccording to claim 24, characterized in that said at least a part of theexhaust gases is previously compressed, after which moisture is removed,and then said at least a part of the exhaust gases is additionallycompressed and is subsequently used as said at least a part of saidinjection gas.
 36. The method according to claims 24, or 25, or 26,characterized in that the water is heated by the heat and/or theelectrical energy prior to the water being injected.
 37. The methodaccording to claims 24, or 25, characterized in that said injection gasis heated by the heat and/or the electrical energy prior to saidinjection gas being injected.
 38. The method according to claims 24, or37, characterized in that a pressure and/or a temperature of saidinjection gas are/is established according to a geological-and-physicalcharacteristic and a development stage of the formation.
 39. The methodaccording to claim 24, characterized in that a composition and aquantity of said injection gas are established according to ageological-and-physical characteristic and a development stage of theformation; specifically, said injection gas is treated to a desirablecomposition by reducing concentration of nitrogen in said at least apart of the exhaust gases.
 40. The method according to claim 24,characterized in that said at least a part of the separated gaseousmixture is treated for removal of moisture and/or corrosive substancesprior to said compression.
 41. The method according to claim 24,characterized in that liquid or gaseous substances, includingcombustible substances, are added into the gas-air mixture prior to saidcombustion.
 42. The method according to claim 24, characterized in thatsaid injection gas is treated for removal of moisture and/or corrosivesubstances prior to said injection.
 43. The method according to claim24, characterized in that said injection gas is injected through atleast one production well.
 44. The method according to claim 24,characterized in that said at least a part of the separated gaseousmixture is separated to produce nitrogen and/or carbon dioxide, and thenthe nitrogen and/or the carbon dioxide are/is mixed with said at least apart of the exhaust gases, whereupon, the resulting mixture is used assaid at least a part of said injection gas.
 45. The method according toclaims 24, or 26, or 36, characterized in that a pressure and/or atemperature of the water are/is established according to ageological-and-physical characteristic and a development stage of theformation.
 46. A system for recovery of hydrocarbons from ahydrocarbon-bearing formation, the system comprising: a power plant withan electrical generator, the power plant having an exhaust gas outletand being adapted to be in fluid communication with at least oneproduction well; an injection means having an outlet adapted to be influid communication with at least one injection well; characterized inthat the power plant comprises a gas engine, or a gas turbine engine, ora gas-diesel engine, any of said engines is adapted to discharge exhaustgases, which comprise nitrogen and carbon dioxide as their components;the electrical generator being connected via mechanical drive means withthe gas engine, or the gas turbine engine, or the gas-diesel engine; andthe exhaust gas outlet being in fluid communication with an inlet ofsaid injection means.
 47. The system according to claim 46,characterized in that it further comprises a separator, the power plantbeing in additional fluid communication with said production wellthrough the separator.
 48. The system according to claim 46,characterized in that the power plant has more than one exhaust gasoutlet.
 49. The system according to claim 46, characterized in that saidinjection means comprises a compressor.
 50. The system according toclaim 46, characterized in that it further comprises a gas-holderadapted to be in fluid communication with the inlet of said injectionmeans.
 51. The system according to claim 46, characterized in that itfurther comprises a pump for injecting water, the pump having an outletadapted to be in fluid communication with at least one injection well.52. The system according to claims 46 or 47, characterized in that itfurther comprises means for preparing a gaseous mixture, the power plantbeing adapted to be in fluid communication with said production welland/or with the separator through said means for preparing a gaseousmixture.
 53. The system according to claim 46, characterized in that itfurther comprises a waste-heat boiler adapted to be in fluidcommunication with the exhaust gas outlet.
 54. The system according toclaim 46, characterized in that the outlet of said injection means isadapted to be in fluid communication with at least one production well.55. The system according to claims 46 or 48, characterized in that itfurther comprises means for separating gases, said means for separatinggases is adapted to be in fluid communication with said injection meansand with the exhaust gas outlet.
 56. The system according to claims 46or 48, characterized in that it further comprises means for purifyingthe exhaust gases, said means for purifying the exhaust gases is adaptedto be in fluid communication with said injection means and with theexhaust gas outlet.
 57. The system according to claim 46, characterizedin that the power plant further comprises a cooling system with a heatexchanger.
 58. The system according to claims 46 or 52, characterized inthat said means for preparing a gaseous mixture is further adapted to bein fluid communication with said injection means.
 59. The systemaccording to claims 46 or 53, characterized in that the waste-heatboiler is further adapted to be in fluid communication with saidinjection means.
 60. The system according to claims 46, or 51, or 53,characterized in that the waste-heat boiler is further adapted to be influid communication with the pump.
 61. The system according to claims46, or 51, or 57, characterized in that the heat exchanger is furtheradapted to be in fluid communication with said injection means and/orthe pump.
 62. A system for recovery of hydrocarbons from ahydrocarbon-bearing formation, the system comprising: a power plant withan electrical generator, the power plant having an exhaust gas outletand being adapted to be in fluid communication with at least oneproduction well through a separator; an injection means having an outletadapted to be in fluid communication with at least one injection well;characterized in that the power plant comprises a gas engine, or a gasturbine engine, or a gas-diesel engine, any of said engines is adaptedto discharge exhaust gases, which comprise nitrogen and carbon dioxideas their components; the electrical generator being connected viamechanical drive means with the gas engine, or the gas turbine engine,or the gas-diesel engine; and the exhaust gas outlet being in fluidcommunication with an inlet of said injection means.
 63. The systemaccording to claim 62, characterized in that the power plant is inadditional fluid communication with said production well.
 64. The systemaccording to claim 62, characterized in that the power plant has morethan one exhaust gas outlet.
 65. The system according to claim 62,characterized in that said injection means comprises a compressor. 66.The system according to claim 62, characterized in that it furthercomprises a gas-holder adapted to be in fluid communication with theinlet of said injection means.
 67. The system according to claim 62,characterized in that it further comprises a pump for injecting water,the pump having an outlet adapted to be in fluid communication with atleast one injection well. with said production well and/or with theseparator through said means for preparing a gaseous mixture.
 69. Thesystem according to claim 62, characterized in that it further comprisesa waste-heat boiler adapted to be in fluid communication with theexhaust gas outlet.
 70. The system according to claim 62, characterizedin that the outlet of said injection means is adapted to be in fluidcommunication with at least one production well.
 71. The systemaccording to claims 62 or 64, characterized in that it further comprisesmeans for separating gases, said means for separating gases is adaptedto be in fluid communication with said injection means and with theexhaust gas outlet.
 72. The system according to claims 62 or 64,characterized in that it further comprises means for purifying theexhaust gases, said means for purifying the exhaust gases is adapted tobe in fluid communication with said injection means and with the exhaustgas outlet.
 73. The system according to claim 62, characterized in thatthe power plant further comprises a cooling system with a heatexchanger.
 74. The system according to claims 62 or 68, characterized inthat said means for preparing a gaseous mixture is further adapted to bein fluid communication with said injection means.
 75. The systemaccording to claims 62, or 67, or 69, or 73, characterized in that thewaste-heat boiler and/or the heat exchanger are/is further adapted to bein fluid communication with said injection means and/or with the pump.